This chapter examines public diplomacy as a foreign policy instrument for the contemporary world. Public diplomacy has enjoyed a revival over the past decade, beginning with the aftermath of the terrorist attacks of 11 September 2001. Within a few years public diplomacy had become the hottest topic on the diplomacy studies agenda, giving rise to robust new debate about the role and relevance of publics and public opinion in the conduct of foreign policy. The chapter first traces the origins and modern evolution of public diplomacy before discussing its theoretical foundations, with particular emphasis on its soft power underpinnings and constructivist tendencies. It also explores key approaches and instruments to illustrate the broad diversity of a project of public diplomacy. Finally, it assesses the role of new media technologies in extending the reach of public diplomacy and drawing foreign policy more than ever into the public domain.