From the viewpoint of carrying out multi-disciplinary studies between economics and other social sciences, Pareto's theories are especially important as they are the core of contemporary orthodox economics. His sociology is constructed very differently from his economics. First the former deals with non-rational social behaviour of human beings, whilst the latter with rational behaviour; secondly, in the methodology the former is empirical and inductive, while the latter is logical and deductive. The present volume is a revamping of works by two authorities on Pareto. It combines Alfonso de Pietri-Tonelli's address to the Italian Association for Advancement of Science on the occasion of the tenth anniversary of Pareto's death with selected chapters of Vilfredo Pareto, sa vie et son oeuvre, Payot, Paris, 1928 by G.H. Bousquet.