The theory and practice of the revolutionary working-class movement. The basic theory or world viewpoint of the proletariat propounded by Marx and Engels, and further developed by Lenin and Stalin.

"Marxism is the system of the views and teachings of Marx. Marx was the genius who continued and completed the three chief ideological currents of the nineteenth century, represented respectively by the three most advanced countries of humanity; classical German philosophy, classical English political economy, and French Socialism combined with French revolutionary doctrine"..."The main thing in the teaching of Marx is the elucidation of the world-wide historical role of the proletariat as the builder of a socialist society" (Lenin).