Forty years ago, on January 1st 1959 a general strike paralysed Cuba and forced dictator Batista to flee the country. In a few days the July 26 Movement guerrillas, led by Fidel Castro and Ernesto Che Guevara entered the capital Havana and were received as heroes by the masses. The Cuban revolution had succeeded. What was the programme of that movement? What was the social basis of that revolution? In order to understand these and other questions we must look back a few years.