In this chapter, the concept of institutionalization is addressed as two sides of a process. On one side and as originally conceived, institutionalization theory is applied to organizations and seeks to articulate how they become socially accepted and successful, with their existence and activities legitimized. On the other side, institutionalization is applied to public relations as a function to examine whether it is becoming institutionalized within organizations, recognized as important for organizational life and success, and to what extent it has become a strategic function of the organization itself. The chapter consists of four parts. First, the basic concepts of old and new institutionalization theory are discussed with a number of themes identified, in order to explore the process that organizations go through to be recognized as legitimate. This sets the scene for a discussion, in the second section, of the institutionalization of the public relations function within organizations using a number of empirical studies as an evidence-base to demonstrate progress. Part three considers how the institutionalization of public relations supports the institutionalization of the whole organization within the economic and social context. Finally the fourth section draws conclusions from these considerations opening up pointers to areas for further progress and research.