A license is a promise not to sue, wrapped in a set of conditions, and almost every dispute about one turns on a boundary the parties never drew clearly. This article explains what a license actually transfers, the difference between exclusive and non-exclusive grants and why that difference determines who may sue infringers, and the scope terms — field of use, territory, term, and permitted purposes — that define the deal. It covers royalties and the audit rights that make them meaningful, improvements and grant-backs, sublicensing, and the trademark quality-control obligation whose absence forfeits the mark. It addresses what happens when a licensee wants to challenge the validity of what it licensed, when a licensor goes bankrupt, and when a product is sold rather than licensed. Examples follow a university spin-out, a software vendor, and a consumer brand.