The documents collected here have already been published earlier, partly in Lenin's Works, partly in Lenin's Collections. Some documents given in the annexes were reprinted from the Menshevik Iskra in 1904-1905. All these documents clearly and convincingly outline the international significance of the split at the Second Congress, the role of Bolshevism on the world stage since its inception, and, finally, Lenin's leading role in the fight against international opportunism and its variety - centrism and with the fluctuations and mistakes of the left from the Second International 30 years ago.