Abstract. We examine the role of transactional memory from two perspectives: that of a programming language with atomic actions and that of implementations of the language. We argue that it is difficult to formulate a clean, separate, and generally useful definition of transactional memory. In both programming-language semantics and implementations, the treatment of atomic actions benefits from being combined with that of other language features. In this respect (as in many others), transactional memory is analogous to garbage collection, which is often coupled with other parts of language runtime systems.