Patents, along with the related systems of utility models and plant breeders’ rights, are the forms of intellectual property most closely associated with technological innovation. Some form of patent system is found in essentially all modern states, and patents have become a ubiquitous feature of the global legal and technical environment. Patents and related rights are therefore highly dynamic areas of law, displaying constant evolution of doctrine simultaneously in multiple jurisdictions. The shifting diversity of national approaches offers an opportunity to consider how characteristic themes and problems of patent law have been approached from different perspectives, and lend a sense of better, worse, and alternative solutions to the problem of prompting technical innovation. Consequently, this chapter surveys particular doctrinal problems in patent law and allied laws, uses them to illustrate both broad theoretical issues endemic to such laws, and ties those issues to ongoing controversies that have attracted widespread interest.