Agusti Nieto-Galan argues that chemistry in the twentieth century was deeply and profoundly political. Far from existing in a distinct public sphere, chemical knowledge was applied in ways that created strong links with industrial and military projects, and national rivalries and international endeavours, that materially shaped the living conditions of millions of citizens. It is within this framework that Nieto-Galan analyses how Spanish chemists became powerful ideological agents in different political contexts, from liberal to dictatorial regimes, throughout the century. He unveils chemists’ position of power in Spain, their place in international scientific networks, and their engagement in fierce ideological battles in an age of extremes. Shared discourses between chemistry and liberalism, war, totalitarianism, religion, and diplomacy, he argues, led to advancements in both fields.