This document provides an overview of market entry and monopolistic competition. It includes: 1) How market entry decreases price and profits for existing firms by shifting their demand curves to the left. Entry continues until economic profits reach zero in long-run equilibrium under monopolistic competition. 2) The key features of monopolistic competition, which include many firms selling differentiated products with no barriers to entry. Firms differentiate their products through attributes like location. 3) A comparison of monopolistic competition and perfect competition, noting that under monopolistic competition firms operate where price exceeds marginal cost while earning only normal profits in the long-run.