The introductory chapter presents the key features of the historical and philosophical analysis of the cosmic microwave background (CMB) radiation, focusing on little known alternative explanations to the Hot Big Bang model that ultimately became the standard interpretation of the CMB. The book challenges the common perception of a swift consensus on the CMB’s explanation by revealing multiple valid alternative hypotheses that are largely forgotten today. It argues this has hindered a comprehensive understanding of the history and methodology of cosmology, as well as the ability to draw important philosophical lessons for contemporary cosmological research. The chapter emphasizes the need to understand the epistemic role of the CMB in cosmology and its implications for addressing criticisms of the field. It highlights the diverse range of alternative theories proposed and suggests revisiting these theories may yield valuable ideas and conjectures for modern cosmology. It emphasizes that overlooking alternatives can impede progress. The discussion covers various aspects, from the controversial beginnings of physical cosmology to the characterization of the orthodox interpretation of the CMB, epistemological and methodological concerns, and both moderate and radical alternatives, drawing lessons for the present and future of cosmological research.