Alfred Marshall - founder of the "Cambridge school." His main work, Principles of Political Economics 2012, which appeared in 1890, was reprinted many times and for many decades served as the main textbook on economic theory not only in England, but also in a number of other Western countries. The central place in the book is occupied by the analysis of factors affecting the formation of price: demand, supply, production costs. The theory of marginal utility was developed in it, the concept of elasticity of demand was introduced, three periods of equilibrium of supply and demand are distinguished.