During the last ten or fifteen years of his life, Talcott Parsons (1902–79) discussed religion and secularization in a number of papers and essays. This work was left unfinished; in the last book that he saw into print, Parsons depicted these papers and essays as work-in-progress. This article focuses on Parsons’ approach to secularization in this late work. Building upon his AGIL-scheme, Parsons analyzed the relation between processes of inclusion and increasing differentiation, on the one hand, and secularization at the (...) value-oriented level, on the other. This article presents a reconstruction and an immanent critique of Parsons’ approach, which highlights both its possibilities and its limitations in order to contribute to the development of a contemporary social theory of secularization and religious change. (shrink)