This article was written on the occasion of the 100th anniversary of the Institute for Social Research in Frankfurt am Main, where the Frankfurt School was founded and continues to evolve. From philosophical and interdisciplinary perspectives, the article focuses on the trichotomic characteristics of critical theory, specifically: critique, explanation, and normativity. It looks first at the founding of the Institute for Social Research; second, at the emergence of critical theory at the Institute; and third, at how these ideas evolved. It identifies trichotomy underpinning Horkheimer’s approach to critical theory. In the conclusion, the revisions made to critical theory in the later stages of development are considered.