It is hard to love a troll, and some feel the same way about patent trolls, the pejorative term for a nonpracticing entity (NPE) that sues a company for infringing its patent. Some feel that NPEs, which do not practice the invention covered by their patent, are like mythical trolls, who lived under bridges and collected tolls, even though they did not themselves build the bridge. Harry Potter taught us to love witches, Shrek taught us to love ogres, but notwithstanding Russ Berrie, trolls tend to get a bad rap. Companies like Apple, Microsoft and Canon have all been sued by NPEs, which often obtain jury verdicts in the hundreds of millions of dollars.

The goals of the patent system are to reward inventors and to spur innovation. Many argue that patent trolls satisfy neither goal and that we need legislation to stop what they argue is a parasitic tax on innovation. However, like Shrek's version of ogres, trolls are also like onions, and only by unpeeling their various layers can we learn to understand the different types of patent trolls and appreciate the different ways in which they can help reward inventors and spur innovation.

The entity most commonly referred to as a patent troll is a company that scours the market for patents, buys them, and then sues a host of companies for infringing those patents. The victims of these NPEs are often giants in the electronics, computer and Internet fields, with hosts of lobbyists looking out for their interests. Much of the anti-patent legislation in recent years has been a reaction to such NPEs.