This chapter makes three main arguments. First, ideas and practices of diplomacy have a multi-millennial history – much longer than is generally thought. Second, this long history has been characterised by both continuity and change. As a result, diplomacy has been as much adaptive as resistant to change. And third, that diplomacy is not diminishing in importance. To assess these claims, the chapter first addresses the issue of defining diplomacy, before examining the evolution of diplomacy in terms that may be characterised broadly as pre-modern, modern and postmodern. Finally, the chapter evaluates the relationship between diplomacy and the study of international relations.