Over the past two decades, the scope of technologies that can be patented has been expanded to include many items previously thought unsuitable for patenting, for example, computer software. Today, the U.S. Patent and Trademark Office grants 20,000 or more software patents a year. Conventional...

In the past, non-practicing entities (NPEs) — firms that license patents without producing goods — have facilitated technology markets and increased rents for small inventors. Is this also true for today’s NPEs? Or are they “patent trolls” who opportunistically litigate over software...