The role of chemistry in twentieth-century Spain tells us a lot about the status and the nature of chemistry as a profession in the last century and the ways in which chemists as experts in academia and industry co-constructed different political regimes. In a way, this is a book about a paradox: with chemistry being frequently presented as an apolitical, neutral, objective, technocratic field, it has played a highly political role in our age of extremes, from the German science-based heritage that preceded the First World War to the petrochemical and instrumental revolution in chemistry during the Cold War. Synthetic molecules in the laboratory and on an industrial scale, standard chemical training in specialisations such as inorganic, organic, physical, medical, industrial and technical chemistry (all of them emerging fields in universities during the nineteenth century) and the mass consumption of colorants, drugs and plastics constituted a complex sociotechnical network, in close alliance with political and economic elites, but apparently detached from any moral responsibility. The lessons from the Spanish case can be extrapolated to other countries.