This article revisits the historical development, core debates, and status of comparative psychology, emphasizing its foundational role in understanding behavior and cognition across species. From its origins in Darwinian evolution and behaviorist experimentation to its integration with ethology and emergence into new disciplines, comparative psychology has undergone significant transformations. We explore the methodological and conceptual divergences between behaviorism and ethology, their eventual convergence through the works of Tinbergen and Lehrman, and the discipline’s expansion into related areas, highlighting its transformative growth through cross-species methodologies, feminist contributions, and novel paradigms like bottom-up comparative analysis. Addressing claims of disciplinary decline, we argue that rather than disappearing, comparative psychology has evolved into a multidisciplinary and dynamic field. Empirical evidence demonstrates sustained productivity and interdisciplinary convergence, challenging narratives of obsolescence. The diversification of species studied and questions asked—particularly those incorporating evolutionary and ecological perspectives—highlights the continued relevance and vitality of comparative psychology in the twenty-first century.