The Introduction presents the main historiographical framework of the book, which mainly focuses on the biographies of research school leaders, university professors, internationally distinguished scholars, industrial chemists, policy-makers and chemistry teachers and popularisers in a broad sense, with a particular focus on their role as ‘co-producers of power’. Departing from the analysis of a specific scientific community, at the same time it offers a more general approach to the culture of chemistry in the twentieth century through the international networks chemists created. After describing the state of the art of the history of chemistry and the history of science in Spain in the twentieth century, this Introduction stresses the contribution of this publication to the bigger picture of science in the twentieth century, and also the way in which chemistry and its practitioners shaped science and politics in Spain. It ends with a reflection on the tension between history and memory and the way in which the new presentism and trends of militant history have influenced the writing of this book.