This chapter explores the components of French strategic analysis and decision-making down to the defeat of June 1940. It proposes that the leaders of France had no choice from the mid-1920s onward but to adopt the grand strategy, though not all the operational campaign plans, that they utilized in 1939-40. The French security policy during the 1920s was about thinking of the relationships between diplomatic commitments and military structures, driven by defensive and even idealistic motivations. In the 1930s, Louis Barthou announced that France would take the steps it judged necessary to ensure its security by national means. France needed to hone its military muscles, as well as strap on diplomatic protection. The best-known expression of the military revival at the heart of French grand strategy was the eastern frontier fortifications. However, France was slower than Britain or Germany in developing radar, and its air defence system remained weak right into 1940.