Which is the largest patent-holding company in the world ? (those that buy patents but not invest in them)?

Question

I'm studying the realm of patent-holding companies in the world. I'm interested in finding out the key players in the field, across North America, Europe and Asia. I'm specifically looking at companies that just buy patents off individual inventors and then license them out for other companies, but do not invest in the patents themselves. Would appreciate any advice/guidance. Thanks.

Answer 1

IV -

http://www.intellectualventures.com/

Founded by Nathan Myhrvold (a former top Microsoft executive) IV might be the biggest patent holding company.  They are certainly one of the most notorious.  

Interestingly, they have never filed a lawsuit or enforced any of their patents.  Instead, they have such an arsenal of patents, people are happy to "invest" to ensure they won't be sued.