Tractatus Logico-Philosophicus is the only book-length philosophical work published by the Austrian philosopher Ludwig Wittgenstein during his lifetime. It is an ambitious project to identify the relationship between language and reality and to define the limits of science. He wrote it as a soldier and a prisoner of war during World War I. First published in German in 1921 as Logisch-Philosophische Abhandlung, it is now widely considered one of the most important philosophical works of the twentieth century. Tractatus Logico-Philosophicus was influential chiefly amongst the logical positivists of the Vienna Circle, such as Rudolf Carnap and Friedrich Waismann. It is more difficult to determine the extent of the influence of the ideas of the Tractatus on Bertrand Russell, since it is frequently hard to determine who is influencing whom, but Russell begins his article "The Philosophy of Logical Atomism", by presenting it as a working out of ideas that he had learnt from Wittgenstein.