Introduction For the past few years, researchers have been debating the relative merits of object-oriented languages with classes and inheritance as opposed to those with prototypes and delegation. It has become clear that the object-oriented programming language design space is not a dichotomy. Instead, we have identified two fundamental mechanisms---templates and empathy---and several different independent degrees of freedom for each. Templates create new objects in their own image, providing guarantees about the similarity of group members. Empathy allows an object to act as if it were some other object, thus providing sharing of state and behavior. The Smalltalk-80 TM language, 1 Actors, Lieberman's Delegation system, Self, and Hybrid each take differing stands on the forms of templates 1 Smalltalk-80 TM is a trademark of Par