In this chapter, we share insights and understandings from mathematics education research on internal context variables, which, for the presage-process-product frame for this book, are those characteristics of students or groups of students which affect responses to mathematics teacher behavior. We also connect student internal context to activities or actions of mathematics teachers and to student mathematics learning activities—student experiences that generatively support their internal contexts. Specifically, we trace the evolution of mathematics education research around the concepts of identity, students’ internal cognitive processes of constructing mathematics, and students’ psychosocial constructions of themselves as students of and doers of mathematics. We also highlight and characterize connections between these processes and external contexts such as teacher actions, mathematics learning activities, and student social/historical context.