Does a European patent always entitle its holder to a permanent injunction? This question has sparked vigorous debate in past years but so far remains unresolved. This open access book presents a detailed, practical, and comprehensive test to determine when injunctive relief should be limited on proportionality grounds. The book's 3 parts guide readers from proportionality's normative foundations to its practical applications. Part I argues that, contrary to conventional wisdom, proportionality is not an open-ended balancing test but rather applies the principle of commensurate scope at the remedies stage. Part II offers an in-depth analysis of situations where a permanent injunction risks upsetting that principle. It draws on a unique qualitative study of all US District Court decisions between 2006 and 2020 granting or denying a permanent injunction in patent cases to stake out circumstances where an injunction might have disproportionate consequences. Part III grounds the inquiry in EU law and proposes a proportionality test along three elements: overreach, abuse, and conflicts with third-party rights. The book thus provides a distinctly European response to a global problem. The book is an invaluable resource for practitioners, clerks, and scholars looking not only for the normative, empirical, and legal basis of proportionality in European patent law, but also for guidance on its real-world operation. The ebook editions of this book are available open access under a CC BY-NC-ND 4.0 licence on bloomsburycollections.com.