The problem of secure software licensing is to enforce meaningful restrictions on how software is run on machines outside the control of the software author/vendor. The problem has been addressed through a variety of approaches from software obfuscation to hardware-based solutions, but existent solutions offer only heuristic guarantees which are often invalidated by attacks. This paper establishes foundations for secure software licensing in the form of rigorous models. We identify and formalize two key properties. Privacy demands that licensed software does not leak unwanted information, and integrity ensures that the use of licensed software is compliant with a license -- the license is a parameter of our models. Our formal definitions and proposed constructions leverage the isolation/attestation capabilities of recently proposed trusted hardware like SGX which proves to be a key enabling technology for provably secure software licensing.