Who propounded monopolistic competition first?

Monopolistic competition was first systematically described by economist Edward Chamberlin in his 1933 book "The Theory of Monopolistic Competition." He introduced the concept as a market structure where many firms sell products that are similar but not identical, allowing them some degree of market power. This theory contrasts with perfect competition and monopoly, highlighting the importance of product differentiation. Chamberlin's work laid the foundation for further developments in microeconomic theory regarding market structures.