This chapter’s aim is to explore the reciprocal relationship between career theory and practice and the evolvement of this relationship over more than a century. Classical criteria are described for the evaluation of career theories in terms of their validity and their practical utility. Given the constant development and redevelopment of career theory in response to the changing nature of the world of work, contemporary criteria for evaluating career theory are also considered. The chapter concludes by considering the relevance of career theory for career practice in diverse cultural contexts.