The contributors present a coherent set of case studies of practices, technologies and strategies aimed at the isolation, investigation, manipulation, production, and uses of molecules including vitamins, hormones, blood products, antibiotics, and vaccines. These case studies examine how processes of molecularization were set in motion in the inter-war period, how they were used as a resource in the biomedical ''mobilization'' of World War II, and how new alliances and strategies created as part of the war effort played a central role in the reorganisation of biomedicine in the post-war period.