Pressing "Buy" on a piece of software almost never makes you an owner; it makes you a licensee, and that single legal choice organizes a multi-trillion-dollar industry. This overview explains the machinery behind that choice: why copyright (17 U.S.C. 106 and 117) turns the ordinary act of running a program into a reproduction that needs permission, why the first-sale doctrine pushed the industry from selling copies to licensing them, and how Vernor v. Autodesk decides when a labeled "sale" is really a license. It gives you a small set of lenses for reading any software contract, walks the four commercial models (perpetual, subscription, SaaS, and open source), and explains how courts decide whether a clickwrap or browsewrap deal even formed under ProCD, Specht, Nguyen, and Meyer. It then maps where money and risk hide in the clauses and follows a license across its life from grant to exit. The goal is a conceptual map a founder, an in-house lawyer, a judge, and a curious non-lawyer can all follow, with pointers to UpLaw's deeper drafting and review resources. This is general information, not legal advice.