This thesis explores the impact of the Russian Revolution on the Spanish anarchist movement in the years 1917-24. Initially, anarchists in Spain welcomed the news of the Russian Revolution euphorically. They embraced many aspects of Bolshevik ideology. The anarcho-syndicalist National Confederation of Labour participated in the first congresses of the Comintern and sent two official delegations to Russia. Yet this enthusiasm was short-lived. By the summer of 1921 anarchists began to turn against Soviet Russia. They reaffirmed their libertarian credentials and articulated an anarchist critique of Bolshevism. In June 1922, the Confederation abandoned the Comintern. This thesis traces the curve of enthusiasm followed by scepticism and hostility that characterised the Spanish libertarians’ attitude towards revolutionary Russia. It grounds these developments in the changing Spanish, Russian, and European political contexts, which went from a phase of revolutionary effervescence in 1917-20 to a phase of defeat and stagnation for the labour movement and of counterrevolutionary offensive in 1921-24. This thesis contends that the short anarchist romance with Bolshevism was not a mere misunderstanding brought about by the lack of reliable news on Russia, as much of the historiography has claimed, but represented a genuine rapprochement that had political causes: the attenuation of the divide between radical Marxists and anarchists during the First World War, the feeling of intense enthusiasm and optimism that set in after the Bolshevik victory, and the temptation to capitalise politically on the Russian Revolution and use it to outcompete the Social Democrats. The situation changed drastically after 1921, when Spanish labour experienced sudden defeat in a dispiring international juncture. Anarchists faced the unwelcome competition of the newly created Spanish Communist Party, which posed as the official representative of the Comintern in Spain. In this context, optimism turned into bitterness, preparing the ground for the turn against the Bolsheviks.