This chapter presents a panoramic analysis of the roots and landmarks of the Latin American critical scientific tradition, explaining the historical conditions—from colonial times to 21st-century society—that determined the distinct periods of the Latin American social medicine/collective health movement, its philosophy, and its ethics. It explains how opposing perspectives and methodological differences arose during those periods, creating a paradigm clash that expresses the interests and views of scholars and decision-makers adhering to different philosophical and practical postures. It describes the fundamental influence in the conceptual and practical shaping of epidemiology of local specific conditions and pressures and also highlights the fundamental influence of and parallelism with outstanding contributions from the North. This chapter provides English-speaking audiences firsthand knowledge of an innovative scientific tradition, explaining its substantial contributions and potentialities for health transformative research, teaching, and community-based agency.