Revolutionary Marxism in Spain, 1930-1937 examines the impact of Trotsky’s politics upon those Spanish communists who dissented from the ‘general line’ of Moscow in the midst of the Spanish Civil War. Exploring the ideas of leading POUM figures, and their complex relationship with Trotsky, Sennett finds that the Russian dissident held more sway in the party than many of the POUM’s historians admit. Deeply engaged with the broader scholarly debates around the role of the POUM in the Spanish Civil War and Revolution, especially in regards to the Popular Front, Sennett draws heavily upon Spanish sources to present and explain the POUM’s political ideas in order to understand why the party adopted the positions it did.