The growing secondary market for patents is a relatively recent phenomenon. Understanding this unusual and developing market is necessary to navigating it effectively. This Article surveys the marketplace, identifies its key players, and notes some of the unique challenges presented in patent sales. Patents are unique assets with differing impacts in different hands. They are susceptible of effective valuation only by specialists—yet most patents are not worth such costly effort and investment. This Article explores how this vibrant marketplace continues to adapt to value these unique assets more efficiently and to deal with imperfect information in individual transactions.