Universities and companies are rushing to the patent office in record numbers to patent nanotechnology inventions. This rush to the patent office is so significant that many law firms have established nanotechnology practice groups and the U.S. Patent and Trademark Office has now created a new technology class designed to track nanotechnology products. Three big differences between the emerging science of nanotechnology and other inventions make the role of patents more significant in this arena than elsewhere. First, this is almost the first new field in a century in which the basic ideas are being patented at the outset. In many of the most important fields of invention over the past century--computer hardware, software, the Internet, even biotechnology--the basic building blocks of the field were either unpatented or the patents were made available to all users by government regulation. In others, patents were delayed by interferences for so long that the industry developed free from their influence. In nanotechnology, by contrast, companies and universities alike are patenting early and often. A second factor distinguishing nanotechnology is its unique cross-industry structure. Unlike other new industries, in which the patentees are largely actual or at least potential participants in the market, a significant number of nanotechnology patentees will own rights not just in the industry in which they participate, but in other industries as well. This overlap may significantly affect their incentives to license the patents. Finally, a large number of the basic nanotechnology patents have been issued to universities, which have become far more active in patenting in the last twenty-five years. While universities have no direct incentive to restrict competition, their interests may or may not align with the optimal implementation of building-block nanotechnology inventions. The result is a nascent market in which a patent thicket is in theory a serious risk. Whether it will prove a problem in practice depends in large part on how efficient the licensing market turns out to be.