This document summarizes different market structures and concepts related to imperfect competition. It discusses monopolistic competition, oligopolies, and monopolies as types of imperfect competitors in selling. It also covers monopsonies, oligopsonies, and monopsonistic competition as types of imperfect competitors in buying. The key characteristics and profit-maximizing behavior of each market structure are described. The document also provides examples of imperfect competition in agricultural input and output markets, and discusses some governmental regulatory measures used to address the adverse effects of imperfect competition.