The diffusion of technologies across firms is a key driver of aggregate productivity growth. A large number of studies focus on technological adoption, the speed of diffusion, and emerging productivity differences across firms. This column examines the adoption of mechanised cotton spinning in France during the Industrial Revolution to study the short-run and long-run effects on firm productivity. It finds that firm productivity gains from this technology materialised slowly in the 19th century, consistent with the need to establish the complementary organisational practices to efficiently operate the cotton mills.