Teacher design practice is simultaneously a cognitive process and a socially situated activity that occurs within complex educational ecosystems. To fully understand this practice, researchers need theoretical frameworks that can capture both its psychological and sociological dimensions. This chapter presents four complementary theoretical lenses for analysing teacher design work: Activity Theory, case-based reasoning, Technological Pedagogical Content Knowledge (TPACK), and the Theory of Practice Architectures. Activity Theory provides a systemic view of design work within educational contexts. Case-based reasoning illuminates how teachers develop and apply design expertise. TPACK identifies the specific knowledge domains teachers draw upon, and the Theory of Practice Architectures reveals how cultural-discursive, material-economic, and social-political arrangements enable or constrain design practice. When integrated, these frameworks can reveal how teachers’ individual knowledge and experiences interact dynamically with institutional contexts to shape design decisions, while also highlighting how collaborative practices and professional communities can either enhance or inhibit innovative design work. These frameworks can help researchers better understand how teachers engage in design work, what shapes their decisions, and how to support their development as designers of learning experiences. The chapter demonstrates how these frameworks can be used individually and in combination to analyse teacher design practice and inform improvements in educational practice and student learning outcomes.