Pareto's Manual of Political Economy, first published in 1905, introduced the analytical approach which has characterised a significant part of twentieth century economic theory. In particular, the Manual examined the ordinal representation of the individual choice, the issue of the general economic equilibrium and the Pareto optimality criterion for evaluating economic efficiency. The Manual also contained analyses of production, non-linear prices, non-competitive markets and the competition process, which have not yet been fully developed in modern mainstream economics.