LinkedIn remains the largest online professional network by far. According to an August 2009 newsletter from the National Contract Management Association, LinkedIn’s marketing statistics boasted a membership of 35 million users. This number included 750,000 senior executives, personnel from all of the Fortune 500 companies, an average user age of 41, and an average household income of $109,000. LinkedIn has grown significantly in recent years; as of December 2013, LinkedIn’s press page stated it had more than 259 million registered members. Click here for LinkedIn’s guide to professional networking online and tips on creating an effective student LinkedIn profile.

For those seeking a more specific community of professionals, these niche online networking sites are worth a look.

XING is a European business network. According to the site, it has more than 7 million members from more than 200 countries.

Biznik is a community of entrepreneurs and small businesses dedicated to helping each other succeed. Whereas businesses use Facebook for connecting with customers, businesses use Biznik for connecting with other businesses.

FemTechNet is a network of hundreds of scholars, students, and artists who work on, with, and at the borders of technology, science, and feminism in a variety of fields including Science and Technology Studies (STS), Media and Visual Studies, and Art.

Cofoundr is a network for entrepreneurs, programmers, designers, investors, and other individuals involved with starting new ventures.

E.Factor is an online community and virtual marketplace designed for entrepreneurs, by entrepreneurs.