Slides and handout from AEA 2019 presentation. Twenty-eight years after Shadish, Cook, and Leviton (1991) asked “What do we mean by theory?” the question remains unanswered, leading many to decry the confusion resulting from inconsistent use of the term theory within the field. To date, few evaluation scholars provide a concrete definition for theory, most resorting to general dictionary definitions or discussing what theory does rather than what it is. This lack of clarity and consensus in the meaning of theory threatens the field’s legitimacy and may perpetuate divisions between practitioners and theorists. Here, I address three questions: What is theory?, Why theory?, and What is the connection between theory and practice?. After repositioning evaluation theory within Aristotle’s knowledge tree, I present a conceptual framework for theorizing evaluation and a conceptual map for a descriptive theory of evaluation which taken together resolve the confusion over theory and its relevance to practice.