Switch reference is a grammatical process that marks a referential relationship between arguments of two (or more) verbs. Typically it has been characterized as an inflection pattern on the verb itself, encoding identity or non-identity between subject arguments separately from traditional person or number marking. In the 50 years since William Jacobsen’s coinage of the term, switch reference has evolved from an exotic phenomenon found in a handful of lesser-known languages to a widespread feature found in geographically and linguistically unconnected parts of the world. The growing body of information on the topic raises new theoretical and empirical questions about the development, functions, and nature of switch reference, as well as the internal variation between different switch-reference systems. The contributions to this volume discuss these and other questions for a wide variety of languages from all over the world, and endevaour to demonstrate the full functional and morphosyntactic range of the phenomenon.