In Volume One:

The Communist Manifesto by Karl Marx and Frederick Engels

Socialism: Utopian and Scientific by Frederick Engels

The State and Revolution by V I Lenin

The Transitional Programme by Leon Trotsky

In Volume Two:

Wage Labour and Capital by Karl Marx

Value, Price and Profit by Karl Marx

"Left-Wing" Communism: An Infantile Disorder by V I Lenin

In Defence of October by Leon Trotsky

Stalinism and Bolshevism by Leon Trotsky