Prototalk is an environment for teaching, understanding, designing, and prototyping object-oriented languages with a prototype-based paradigm. It allows different prototype-based OO languages like Self and NewtonScript to be expressed using the same syntax. Prototalk represents each language using a subclass and executes programs by sending an evaluate message. It has a minimal core that can express the most general semantics and is extensible so new languages can be implemented efficiently.