LinkedIn is an online social network for business professionals. It's different than other social networking sites like MySpace and Facebook because it's designed specifically for professional networking -- finding a job, discovering sales leads, connecting with potential business partners -- rather than simply making friends or sharing media like photos, videos and music.

Image courtesy LinkedIn LinkedIn home page

Online social networking has exploded in recent years, largely due to the massive popularity of MySpace and Facebook. In August 2007 alone, MySpace had more than 60 million unique visitors and Facebook attracted 19 million, a growth rate of 23 percent and 117 percent, respectively, from a year earlier [source: Mashable].
Online social networks are Web sites where users create personal profiles, search for "friends" or "contacts," and create extensive networks of connections. There are more than 300 social networking sites in existence built around many different themes: video-sharing sites, photo-sharing sites, social bookmarking sites, music-sharing sites, blogging communities, all-purpose community sites like MySpace and professional networking sites like LinkedIn.
LinkedIn was co-founded in May 2003 by Reid Hoffman, Allen Blue, Jean-Luc Vaillant and Konstantin Guericke. The site was the brainchild of Hoffman and Guericke, Stanford graduates who began planning their online professional network in the late 1990s [source: USA Today].
With more than 15 million members by October 2007, LinkedIn is one of the fastest-growing online social networks in the world. Traffic rose 323 percent from July 2006 to July 2007, making the site the No. 1 online destination for professional networking [source: Tech Crunch]. Average users typically collect two or three dozen connections, while a handful of "superusers" have amassed as many as 34,000 [source: Entrepreneur].
In this HowStuffWorks article, we'll explore all of the features of LinkedIn and how to use them. We'll also explain who uses LinkedIn, why it's different from other social networking sites, and whether or not it actually works.
Let's start with a step-by-step explanation of how to use LinkedIn.
To start using LinkedIn you need to register and create a profile page. During registration, you'll be asked for some basic personal information: name,
e-mail address, location, current employer and where you went to college. Then you'll be prompted to fill out more detailed information on your profile page.

Image courtesy LinkedIn LinkedIn basic information page

A LinkedIn profile reads like a professional résumé. The focus is on employment and education history, not a list of hobbies and favorite movies. To fill out your profile page, you'll begin by creating separate entries for each of your current and former jobs -- job title, employer, industry, dates and a short description of what the job entailed.

Image courtesy LinkedIn LinkedIn summary, experience and education page

Education experience works the same way. You'll create separate education entries for every institution you attended after high school. Education entries include the school's name, degree earned, years attended, awards won and any other notes you'd like to add. LinkedIn will use all of this employment and education history later on to help you search out former and current colleagues and classmates.
Employment and education history are the basics of the profile page. You can also fill out a summary, which is a short description of your professional experience and skills, and post a profile picture. There's also a section to list any Web sites that you're associated with, both personal and professional, and a space for a short list of interests, affiliated groups and honors.
Now let's see how to find people to join your network.
Now that you've filled out your LinkedIn profile page, the second step is to search out and connect with other members of the site. LinkedIn provides several methods for searching out contacts:

• Upload your e-mail contacts
• Colleague search
• Classmate search
• Name search
• Advanced search

If you have a Gmail or AOL e-mail account, you can type in your e-mail address and password and LinkedIn will automatically find all of your e-mail contacts who are already members of the site. You can also use LinkedIn's "Find Contacts Wizard" to upload contacts from Microsoft Outlook or any other address book software.

Image courtesy LinkedIn LinkedIn network page

Once you've uploaded your contacts, you then can select which of those LinkedIn users you'd like to invite to become members of your network. You can also use this opportunity to invite all of your non-LinkedIn contacts to join the site.
Using the employment information from your profile page, LinkedIn will also show you all of your past and present colleagues who are members of the site. Just like your e-mail contacts, you then can choose which colleagues you'd like to invite to join your network.
The same goes for your education history. Using the classmate search, LinkedIn will show you a list of all of the current LinkedIn members who attended your college or graduate school at the same time you did. You can also narrow down the search results to only those who graduated in your class.
If you click on the "People" section of the LinkedIn Web site, you can conduct a name search or an advanced search. With a name search, you enter either a full name or just the last name of the person you're looking for and LinkedIn will give you a list of all current members who share that name.

Image courtesy LinkedIn LinkedIn search

An advanced search allows you to search for LinkedIn members using several different criteria: keywords, name, title, company, location and industry. Advanced searches could help you find an "inside contact" at a company to use as a sales lead or can give you the inside edge on a job application.
The third step -- after you've built your profile and found people you know -- is to turn these contacts into "connections."
Finding classmates, colleagues and friends is just the beginning. To leverage the real power of LinkedIn -- gaining access to your connections' connections -- you have to invite these people to join your network.
On LinkedIn, the people who are part of your network are called your "connections." A connection on LinkedIn is different than a "friend" on MySpace or Facebook. Connections imply that you know the person well or that they're a trusted business contact. LinkedIn warns against adding complete strangers to your network, or accepting an invitation from someone you don't have a trusted relationship with. We'll talk more about this later.

Image courtesy LinkedIn A LinkedIn invitation

To turn a contact into a connection you need to invite that person to join your network and they need to accept. Likewise, for another person to add you to their network they need to invite you and you need to accept. Regardless of who invites who, when an invitation is accepted, both parties are automatically added to each other's list of connections.
There are several ways to send an invitation through LinkedIn. If you found the contact during a colleague or classmate search, or he or she is already one of your e-mail contacts, then the process is simple. You click a check box next to the name or names of the people you want to invite and press a button that says "send invitations." LinkedIn will send a generic invitation unless you specify that you want to add a personal note.
If you found the contact through a name search or advanced search, LinkedIn has to verify that you really know this person before it will allow you to send the invitation. LinkedIn will ask how you know this person: as a colleague, classmate, business partner, friend, groups or association, other, or "I don't know [name]." If you choose "friend" or "other," LinkedIn will ask for the contact's e-mail address. If you choose "I don't know [name]," LinkedIn will not allow you to send the invitation. For the other categories, you'll be asked to indicate through which job, school or organization you know the contact.
It's also possible to block or filter the invitations you receive through LinkedIn. You can choose to only be notified of invitations that come from people who know your e-mail address or who are already on your e-mail contact list. You can also remove a connection after you've accepted their invitation. You just go to your list of connections, check the box next to the people you want to remove and press the "remove connections" link. Don't worry, LinkedIn won't tell them.
LinkedIn has rules for contacting people within your network and the network at large.
The people who have accepted an invitation to join your network are called your "direct connections." They're described as being one degree away from you on the greater LinkedIn network. You're free to contact those people directly by clicking the "send e-mail" button on their profile pages.
All of your direct connections' connections are two degrees away from you on the LinkedIn network. And their connections are three degrees away. Technically, all LinkedIn members that are connected to you up to three degrees away are part of "your network." But you can use e-mail to contact only your direct connections. To contact second and third degree members requires special LinkedIn tools called introductions, InMail or OpenMail.

Image courtesy LinkedIn In order to use LinkedIn InMail, you'll need to upgrade your account.

LinkedIn provides five introductions with a free account. You can buy more introductions by upgrading to a premium account. Here's how introductions work:

1. Find a direct connection who is connected to the person you want to contact.
2. Send your direct connection an introduction message asking that he forward it to his connection.
3. Your direct connection has the option of not forwarding the introduction.
4. If he chooses to forward it, the recipient has the option of not accepting the introduction.
5. If the introduction is accepted, it's not the same as joining a network. You'll still have to send that member an invitation asking him to join your network. That may require that he give you his e-mail address for confirmation.

InMail and OpenLink are both available only to premium account holders who pay monthly or annual subscription fees for the service. InMail is LinkedIn's internal messaging system. It allows you to directly contact anyone on the LinkedIn network without an introduction.
OpenLink is a service that allows you to receive OpenLink messages from anyone on the LinkedIn network. The sender of the OpenLink message doesn't have to pay anything. The advantage for you is that you can keep your e-mail address and other contact information private while opening yourself up to a wider range of contacts and connections.
Now let's explore how LinkedIn is different from other social networking sites.
LinkedIn is different than other social networking sites in that it's designed solely for the purpose of professional networking. As we said earlier, a LinkedIn profile page is essentially an online résumé. You can't post photos (other than your profile photo). You can't host a blog. You can't embed your favorite YouTube videos or playfully "poke" your friends. You can't personalize the colors or layout of your profile page or search for "single females, age 25-30" in your area.

Brian Arch/WireImage LinkedIn CEO Dan Nye and a guest walk the Webby Awards red carpet on June 5, 2007.

The clean, streamlined design of a LinkedIn profile page is part of a conscious effort to put a professional polish on social networking sites. There have been several high-profile cases in the news of people being passed up for jobs, or even losing jobs, because of a poorly chosen photo or comment on their blog, MySpace or Facebook page. LinkedIn CEO Dan Nye commented that the site is designed to present its members in "a professional way on the Internet" [source: LinkedIn].
We also mentioned that a connection on LinkedIn implies more than a casual acquaintance. LinkedIn recommends that all connections be viewed as potential professional or personal references. You should feel confident that all of your connections would give you a positive recommendation to a future employer or a kind introduction to other members of their network. Also, once someone becomes your connection, they'll have access to all of your other connections. You don't want to connect with anyone who will embarrass or misrepresent you with your other connections.
LinkedIn differs from its closest competition, Facebook, because Facebook is group-based while LinkedIn is much more focused on the individual and his accomplishments. For example, Facebook automatically assigns members to "networks" based on their physical location and which college they attended. This is most likely a holdover from the days when Facebook was only for college students. Facebook members can then easily sign up with thousands of other groups and networks formed by Facebook members.

Image courtesy LinkedIn LinkedIn Groups

LinkedIn has something called LinkedIn Groups, but the process of creating and joining a group is more involved than Facebook or most other social networking sites. LinkedIn has a special review panel that accepts new group requests only from professional organizations, alumni groups, professional alumni organizations, industry conference and similar business-oriented groups. And once a group is added, the group's manager is in charge of accepting or rejecting all applications to join the group.
LinkedIn also operates using a different business model than most social networking sites. There are some Google ads on LinkedIn, but no corporate sponsors or other commercial ads as of yet. In comparison, MySpace was pulling in nearly $25 million a month in online ad revenue by February 2007 [source: Media Week]. And Facebook announced an advertising scheme in early November 2007 that will bring highly targeted corporate ads to the site from names like Coca-Cola, Blockbuster and Verizon Wireless [source: PC World].
Instead, LinkedIn makes money in two basic ways. First, the site charges users for certain services. If you want to send more than five introductions, you have to upgrade to one of the premium accounts (Personal Plus, Business or Pro). Same goes for sending InMail or receiving OpenLink messages. Posting job openings costs money on LinkedIn, as do other site services like reference searches and expedited customer service.
But the way LinkedIn really makes the big bucks is through LinkedIn Corporate Solutions, a powerful tool for recruiters and corporate headhunters. When a registered LinkedIn user adds his professional and educational experience to his profile page, he's adding his personal information to the ever-expanding LinkedIn professional database. For a steep annual subscription fee (as high as $100,000 to $250,000 for some companies), LinkedIn Corporate Solutions supplies recruiters and headhunters with enhanced search tools and management software to find the most qualified "passive candidates" [source: HR.com].
A passive candidate is someone who already has a job and isn't actively looking for a new one. According to LinkedIn, a passive job candidate generally has higher qualifications than the average active job-seeker [source: LinkedIn]. Corporate recruiters search out skilled workers in other companies and try to convince them to switch to another firm. LinkedIn estimates that more than 100,000 of its members are professional recruiters [source: Workforce.com].
Now let's look at who uses LinkedIn and for what purposes.
There are many different audiences for LinkedIn's professional networking services. The first is simply people looking to stay in touch (or get back in touch) with former colleagues and classmates. This is networking at its most basic and most passive. The idea is that someday you might need to leverage the connections in your network to get a new job or find a sales lead. But for now, it's just fun to reconnect with old friends and coworkers and see what they've been up to.
The second audience for LinkedIn is active job-seekers and job posters. LinkedIn has an entire section of the Web site devoted to "Jobs and Hiring." It's free to search for jobs on LinkedIn, but it costs $145 to post a job listing (discounts are available for multiple listings).

Image courtesy LinkedIn LinkedIn Job Search

To search for a job, you fill out a quick search form with a keyword and your desired location. The search results are divided into jobs that have been posted on LinkedIn and jobs that are posted on the Web. Most importantly, LinkedIn organizes the search results by your networked proximity to the job poster. For example, LinkedIn tells you if the hiring manager for Acme, Inc. is only two degrees away from you in your network. That way you can use an introduction to contact the hiring manager directly, perhaps giving you an advantage over other applicants.
If you're hiring, there are ways to use LinkedIn without paying for a job posting. There's a search box on the Hiring and Recruiting page that allows you to search for candidates using keywords. You could also conduct an advanced people search with the keywords and industry experience you desire. Another way is to distribute a new job announcement to your network. This is simply a message sent via LinkedIn to your direct contacts asking if anyone can recommend someone for the open position at your company.
Once you've received some applications through LinkedIn, you could run a reference search (premium account holders only) to see what the applicant's former colleagues say about him or her. The reference search allows you to search by company name and see who worked there during a specific time period.
Another audience, as we've mentioned, is full-time recruiters and headhunters. LinkedIn is a boon for recruiters because it allows them to tap into a tremendous professional database with a simple Web interface. By subscribing to LinkedIn Corporate Services, recruiters get even more tools for finding the best candidates among LinkedIn's 15 million active members.

Image courtesy LinkedIn LinkedIn recruiter page

Salesmen can spend thousands of dollars on targeted business-to-business sales lead lists. With LinkedIn, a salesman can search within his target industry for people who might be interested in his products. Then, either by leveraging an introduction from their existing network, or by contacting directly through InMail, they can make their pitch directly to an inside contact.
Entrepreneurs can use LinkedIn to search out potential business partners, clients and vendors. Also, in a section called LinkedIn Answers, you can ask a question to your network (up to three degrees away). Someone starting a small business could ask for advice from other people in the same industry. Or you could use the LinkedIn Services page to find contractors and specialty workers who have been recommended by other LinkedIn users.
Public relations professionals are always looking for the right contact at newspapers, magazines or television stations to send a targeted press release. By conducting an advanced people search on LinkedIn, they could locate reporters and editors who cover their client's industry and contact them through connections or InMail.
On the flip side, journalists themselves can use LinkedIn to find inside contacts within a company and avoid having to speak with a PR representative first.
Now let's address the big question: does LinkedIn actually work?
Whether LinkedIn works or not depends on what you're using it for. It's most useful when you have a specific task that you're trying to complete, like looking for a job or looking for advice from people in your field [source: B. Mann Consulting]. It's less useful if you're just a passive member who's collected some connections but isn't really in the market for a new job, or in a field that requires much professional networking.
On the most basic level, LinkedIn works really well for reconnecting with past colleagues and classmates. Because LinkedIn has reached a critical mass of 15 million members (and is expected to reach 18 million by the end of 2007), there's a good chance that many of the people you've worked with or went to school with have already signed up.
Beyond the satisfying voyeurism of seeing what old friends (or enemies) are up to, LinkedIn offers its users a way to put this previously invisible network of connections into action. Of course it's fun to get back in touch with old friends, but that's something you can do on a lot of other social networking sites. LinkedIn wants to inspire its users to go beyond fun and get down to business. Whether or not users respond to that challenge will dictate how useful the site becomes for them.
What's clear is that LinkedIn definitely works for recruiters. One recruiting firm we read about spends a little more than $7,000 a year on LinkedIn Corporate Services, but pulls in more than $100,000 in commissions from employees found through the service [source: Work Force]. One recruiter who uses the InMail service to contact prospects directly says he receives a response 90 percent of the time [source: Work Force].
Human nature is such that it's always easier to get a job from someone you know than from a complete stranger. A professional networking tool like LinkedIn has the potential to greatly expand the universe of who you know. A LinkedIn user with 41 connections can have more than 200,000 members in his or her network -- that is, people who are three degrees away or less. When it's time to look for a job, LinkedIn allows you to search for job openings within your network. Instead of cold-calling the office and asking for the hiring manager, you can get an introduction through a mutual friend.
LinkedIn also seems to work for sales leads, particularly if you have a large network of direct connections. We read about a CEO of an online advertising company who used an introduction from one of his direct connections to contact the COO of a potential client and invite him to lunch. The COO responded immediately. He said he didn't have time for lunch, but that he did need a new ad server. They signed a contract two weeks later [source: INC.com].
LinkedIn won't provide salesmen with thousands of leads like a purchased sales lead list, but the leads the site helps generate come with a distinct advantage: the possibility of an inside connection. As an article on Inc.com says, LinkedIn takes cold calls and "warms them up" through shared friends and colleagues [source: Inc.com].

Image courtesy LinkedIn LinkedIn Answers

As for entrepreneurs and small business owners, LinkedIn Answers can be an effective resource for specific business advice and potential partners. Browsing the lists of questions and answers in the "Startups and Small Businesses" sections, we found thoughtful, lengthy answers on subjects as varied as health insurance for small businesses, how to gain customer trust, and how to assemble an IT infrastructure quickly and cheaply. As with any message board system, there will be a fair share of spam and self-promotion, but LinkedIn is adding a new flagging functionality to call attention quickly to such annoyances [source: LinkedIn Intelligence].
But like all social networking sites, LinkedIn has the potential to be nothing more than an amusing time-waster, a way to gather your same old online friends and connections on the latest Web 2.0 craze. LinkedIn, however, is positioning itself as the place where social networkers will go when they get serious about networking [source: USA Today]. The idea is that all those Facebook-crazed college kids will shift over to LinkedIn when real life comes knocking at the door.
To wrap things up, let's talk a little about privacy and hacking concerns regarding LinkedIn.
When a Web site is as popular as LinkedIn, it's easy to get caught up in the excitement of posting a profile page without considering the level of information you're sharing. Unfortunately, by posting too much personal and business information on a site like LinkedIn, you could make yourself vulnerable to social engineering hackers.
Social engineering is the practice of using psychological techniques to persuade people to give up sensitive information like passwords or corporate secrets. Social engineering is an effective way to hack a business network because it targets the weakest link in the system: human beings [source: SearchSecurity.com].
An example of a popular social engineering scam is to call the IT department of a company posing as a frantic, angry executive who has lost his network password and needs it immediately for an important meeting. The IT worker will be so frazzled by the call that he'll give up the password without taking the necessary security precautions [source: Security Focus].
You might think that the information you post on LinkedIn is secure because only members of your network can see full profiles. But LinkedIn is different than some other popular social networking sites like Facebook because it allows search engines like Google to access a version of your profile page called the "public profile." When you create a profile page on LinkedIn, you also create a public page that can be seen by anyone who conducts a relevant Web search.

Image courtesy LinkedIn LinkedIn public profile settings

LinkedIn allows you to adjust your privacy setting for that public profile page, including an option to remove the public profile altogether. You can choose to limit your public profile to your name, location and job, or post the "full view," which is your full profile minus recommendations and contact information. Even in "full view" mode, the public profile page will never list your connections.
Only your direct connections -- one degree away -- can see your list of connections. Ultimately, that puts users in control of their privacy. This is why it's so important to accept LinkedIn invitations only from people you know and trust. If a social engineering hacker knows your name, where you work, where you worked, where you went to school, as well as names of current and former colleagues and classmates, it's much easier for him to come up with a convincing scam. He can use all of this information to win your confidence (where the word "con" comes from) and subtly persuade you to give up information you wouldn't have otherwise shared with a complete stranger.

Image courtesy LinkedIn LinkedIn account settings

LinkedIn allows users to adjust their privacy settings anytime by clicking on the "Accounts & Settings" link at the top of every LinkedIn page. On that page, you can make your name and location invisible to other LinkedIn users. You can control how and if your connections are notified when you make changes to your profile or add new connections. And you can control whether even your direct connections can browse your connections list.
As for LinkedIn's overall privacy policy, the site promises not to share or sell any of your personally identifiable information to partners. It does, however, share other information like your industry or region with Web site partners for advertising purposes. Basically, if you visit one of LinkedIn's partner sites, you might see ads that are targeted to your job or location. If you want to shut off that targeted advertising service, you can do so on the accounts and settings page.