LinkedIn is a social network for business. It's free to join, and the benefits of joining include access to a network of highly mobile and influential people as well as access to discussion groups that contain the very best.

1. On Startups – The Community For Entrepreneurs

On Startups does what it says on the tin. It's a startup community for entrepreneurs and small business owners, with around a quarter of the members describing themselves as business owners. Started in 2007 On Startups has grown fast, there are just under a quarter of a million members of this group making it the largest entrepreneurship community on LinkedIn.

Join now - http://www.linkedin.com/groups?home=&gid=2877

2. TED: Ideas Worth Spreading

TED started life in 1984 as a conference bringing together people from the Technology, Entertainment, Designworlds. Since then its scope has become ever broader and it has an International reputation hence the almost 200,000 members of this group. It's a very intellectual and entrepreneurial group and it's very big on blue-sky-thinking. If you're looking at alternative ways of thinking about business, then there's nowhere better.

Join now - http://www.linkedin.com/groups/TED-Ideas-Worth-Spreading-138801

3. Harvard Business Review

The Harvard Business Review is one of the World's leading business journals and it prides itself in being a business bible for new and alternative business thinking. This official LinkedIn group is run by editors from the HBR and is a must-join group for anyone looking for new business insights and best practices guides.

Join now - http://www.linkedin.com/groups?home=&gid=3044917

4.Innovative Marketing, PR, Sales, Word-of-Mouth & Buzz Innovators

It's a long-winded name but there's plenty of useful discussions on this group. It's LinkedIn's largest Marketing & PR group with over 165,000 members and as you would expect it's a very lively group with over 160 discussions a day on various subjects from email marketing to using social media to generate sales leads.

Join now - http://www.linkedin.com/groups?home=&gid=54066

5.Start-Up Phase Forum

A small community for entrepreneurs and small business owners in the start-up / startup phase of their business to share information and support. The group offers a wealth of information on marketing, SEO, funding, advice, work at home ideas, blogging, finance, recruiting, legal aspects, slogans, branding and so much more

Join now - http://www.linkedin.com/groups?home=&gid=48005