Historiography has paid less attention to cancer than to other diseases. This is probably because its emergence as a major social problem is relatively recent, compared to other diseases that have devastated humanity for centuries. In the last two decades, studies on the cancer from a historical perspective have been increasing. However, this has not been the case in Spain. This volume attempts to remedy this deficiency by studying various aspects that allow us to outline how cancer became a social problem in Spain throughout the 20th century. The chapters explore various aspects. Some of them are cross-cutting and appear in all case studies. One of them is the preponderance of the biomedical approach when conceiving the disease. Another, of great importance, is the constant presence of charitable and philanthropic initiatives at both the local and national levels. Despite some programmatic statements, public healthcare, with all the peculiarities of its development during General Franco’s dictatorship, did not deal with the disease in a specific manner prior to the 1970s. The institutions that were created to deal with the problem were, in most cases, driven by charitable impulses, with the support of local entities. The importance of early diagnosis and the responsibility of the population in this regard, a kind of self-monitoring, is another constant. In addition, the treatment of cancer transformed the way healthcare was conceived with the emergence of new, increasingly sophisticated therapeutic options, with a strong presence of technoscience, around which new specialities were developed. Finally, some chapters also deal with representations of the disease. The authors come from diverse academic traditions, which enriches the approaches used and allows for the use of varied sources.