Although the potential for classroom assessment to support L2 teaching and learning has long been recognized, conceptual frameworks for appraising specific assessment practices and determining how they may be developed has remained elusive. In this chapter, we outline a potential way forward in L2 classroom assessment research and practice that envisions them as existing in a bidirectional, reciprocal relationship. We discuss this through the prism of praxis, as brought to the attention of L2 researchers in the work of Lantolf and Poehner (Sociocultural Theory and the pedagogical imperative in L2 education. Vygotskian praxis and the research/practice divide. Routledge, London, 2014). We begin by identifying the epistemological foundations of much assessment scholarship to date, arguing that these have led, on the one hand, to prescribing assessment practices to teachers (a unidirectional relationship between theory/research and practice), or, on the hand, to documenting existing classroom assessment practices without any attempt to consider them in a broader context or to improve upon them. Following this, our discussion turns to praxis, which represents a unity of theory/research and practice wherein these inform one another and change together. Specifically, theory offers principles and concepts that teachers may draw upon to construct practices in a reasoned manner that is responsive to but that goes beyond firsthand experience. Practice, for its part, serves to identify ways in which theory may need to be revised and expanded. Understood as praxis, general conceptual frameworks of classroom assessment and the ways in which it is practiced in particular contexts must be developed in tandem. We argue that this can be productively pursued through collaboration between assessment researchers and teachers. The chapter concludes with an overview of how praxis is taken up and realized in each of the chapters in the book.