The theory of Permanent Revolution has been associated with Leon Trotsky for more than a century since the first Russian Revolution in 1905. Trotsky was the most brilliant proponent of Permanent Revolution but by no means its sole author. The documents in this volume, most of them translated into English for the first time, demonstrate that Trotsky was one of several participants in a debate from 1903-7 that involved numerous leading figures of Russian and European Marxism, including Karl Kautsky, Rosa Luxemburg, Franz Mehring, Parvus and David Ryazanov. This volume reassembles that debate, assesses it with reference to Marx and Engels, and provides new evidence for interpreting the formative years of Russian revolutionary Marxism.