This classic and highly influential book provides unique insight into ideas of competition and the theory of the firm. First published in 1933, it builds upon the work of Alfred Marshall and Arthur Cecil Pigou and highlights both the real world application and limitations of economics, with a particular emphasis on the risk of providing misleading information to individuals. By setting out ways in which economic practices and tools can be refined, the importance of stating assumptions and finding suitable answers is highlighted. Broader topics, including monopoly equilibrium, the supply curve, price discrimination, marginal net productivity, and monopsony, are also discussed. This book is an important milestone in the history of economics and the development of key economic concepts. It will be relevant to students, researchers, and general readers interested in economic theory and microeconomics. Includes a new foreword from John Eatwell.