Like the ownership of physical property, the issues computer software ownership raises can be understood as concerns over how various rights and duties over software are shared between owners and users. The powers of software owners are defined in software licenses, the legal agreements defining what users can and cannot do with a particular program. To help clarify how these licenses permit and restrict users’ actions, here I present a conceptual framework of software rights and duties that is inspired by the terms of various proprietary, open source, and free software licenses. To clarify the relationships defined by these rights and duties, this framework distinguishes between software creators (the original developer), custodians (those who can control its use), and users (those who utilise the software). I define the various rights and duties that can be shared between these parties and how these rights and duties relate to each other. I conclude with a brief example of how this framework can be used by defining the concepts of free software and copyleft in terms of rights and duties.