This study so far has attempted patiently to reconstruct the major concepts and stages in the development of Horkheimer’s Critical Theory through the late 1930s. Retracing the steps that Adorno followed on his path to Horkheimer and eventually to Dialectic of Enlightenment would require an equally patient reconstruction of his work in the late 1920s and early 1930s – a task that is obviously beyond the scope of this work. Thankfully, scholarship on Adorno is much further advanced than on Horkheimer, so this task has already been attempted by several competent commentators. Here, I would like only to provide an overview of some of the key stages in the development of Adorno’s work and his relationship with Horkheimer, which will make it possible to understand the shift that occurred in the latter’s work in the late 1930s. To speak of a rapprochement between Horkheimer and Adorno in the 1930s may come as a surprise to those unfamiliar with the prehistory of their friendship. Unlike Horkheimer and Pollock, whose remarkable early friendship and symbiotic working relationship – one recalls their nicknames for one another: Horkheimer was the ministre de l’intériuer and Pollock the ministre de l’extérieur – had made them virtually inseparable since the age of fifteen, Horkheimer did not develop a serious friendship and working relationship with Adorno until much later. The secondary literature on Critical Theory has yet to fully examine the important differences that existed between Horkheimer and Adorno in the late 1920s and early 1930s. In what follows, I want to demonstrate in particular how and why Horkheimer and Adorno parted ways theoretically in the late 1920s and early 1930s; how this divergence led to a brief period of estrangement in 1933–4; how Adorno’s debate with Benjamin, a renewed study of Hegel, and his positive reception of Horkheimer’s work in the mid-1930s brought them back together; and how, finally, Horkheimer gradually overcame some of his reservations about Adorno’s work and began to move closer to him theoretically. Despite this gradual rapprochement in the mid-1930s, important theoretical differences remained between them; it was not until after Adorno’s arrival in New York in 1938 and a period of intense collaboration with him that Horkheimer abandoned many of the key assumptions of his early Critical Theory and moved closer to Adorno, thereby setting the stage for Dialectic of Enlightenment. It is crucial to identify the causes of the estrangement between Horkheimer and Adorno and to reconstruct the long and sometimes difficult rapprochement in order to demonstrate that the two authors of Dialectic of Enlightenment came to that work from very different paths and that this work ultimately represented a more significant break with Horkheimer’s early Critical Theory than it did with Adorno’s thought in the 1930s. We will return to Dialectic of Enlightenment in the epilogue.