If you are involved with business, especially if you work for a global, multinational company, chances are good you are already familiar with the social networking site LinkedIn. With 100 million members and growing, LinkedIn is the world’s largest professional network. And unlike a social network like Facebook or Myspace, LinkedIn’s usefulness extends beyond finding that kid you knew in high school (although you can do that too). It focuses on professional relationships and connections, making it nearly indispensable for jobseekers or employers or just someone looking for advice.

LinkedIn helps you to sort contacts into a number of different groups, with the ability to message all or some members of a specific group at once; so that not only can you stay in contact with former and present colleges, you can see the patterns that connect them. And, for companies looking to hire, its usefulness extends beyond message board-type capabilities.

Say you’re a recruiter working at a large company. Your last hire was a huge success, and, wanting to replicate that success, you take a glance at the hire’s LinkedIn profile for other contacts with job histories and experience that match the new opening. Already the company has saved time by finding people who are truly qualified for the position rather than wading through a sea of non- or under-qualified applicants. There is the added bonus that employee referrals have a higher success rate than cold hires.

LinkedIn, which went public in May of 2011, has been as much of a success for its investors as it is for the companies who use its service. After initial estimates predicted a loss in its first quarter of trading, the company posted a surprise profit. LinkedIn’s CEO, Jeff Weiner, plans to build on that forward momentum and further invest in the business — a similar strategy to the one that gave the company its profits — and continue to encourage growth in LinkedIn through programs liked LinkedIn Today, which shares information through “Share on LinkedIn” buttons.

As LinkedIn becomes a more throughly integrated part of professional life, it will likely grow from being simply a helpful tool to an essential component of the workplace.