We identify the patents litigated most frequently between 2000 and 2007,
and compare those patents to a control set of patents that have been
litigated only once in that period. The results are startling. The most
litigated patents are far more likely to be software and telecommunications
patents, not mechanical or other types of patents. They are significantly
different from once-litigated patents in ways that signal their value up
front. And they are disproportionately owned by non-practicing entities
(aka trolls). The results don’t answer all the policy questions; we offer
only one important piece of a larger mosaic. But they have significant
implications for debates over patent reform, since we show both that the
most litigated patents are the most valuable ones and that they are most
commonly in the hands of companies other than the ones building new
products.