The patent system seems in the midst of truly dramatic change. The lasttwenty years have seen the rise of a new business model – the patent troll– that grew to become a majority of all patent lawsuits. They have seen asignificant expansion in the number of patents granted and a fundamentalchange in the industries in which those patents are filed. They have seenthe passage of the most important legislative reform in the last sixtyyears, a law that reoriented legal challenges to patents away from courtsand toward the Patent and Trademark Office (PTO). And they have seenremarkable changes in nearly every important legal doctrine, from patenteligibility to obviousness to infringement to remedies.These changes have prompted alarm in a number of quarters. From the 1990sto the 2000s, as the number of patents and patent troll suits skyrocketed,technology companies and academics worried about the “crisis” in the patentsystem – a crisis of overprotection that might interfere with rather thanpromote innovation. By 2015, as patent reform took effect and the SupremeCourt undid many of the Federal Circuit’s expansions of patent rights, itwas patent owners who were speaking of a crisis in the patent system – acrisis of underprotection that might leave innovators without adequateprotection. Depending on one’s perspective, then, the sky seems to havebeen falling on the patent system for some time.Despite the undeniable significance of these changes in both directions,something curious has happened to the fundamental characteristics of thepatent ecosystem during this period: very little. Whether we look at thenumber of patent applications filed, the number of patents issued, thenumber of lawsuits filed, the patentee win rate in those lawsuits, or themarket for patent licenses, the data show very little evidence that patentowners and challengers are behaving differently because of changes in thelaw. The patent system, then, seems surprisingly resilient to changes inthe law. This is a puzzle. In this article, I document this phenomenon andgive some thought to why the fundamental characteristics of the patentsystem seem resistant to even major changes in patent law and procedure.The results pose some profound questions not only for efforts at patentreform but for the role of the patent system in society as a whole.