This document provides an overview of monopoly market structure. It defines monopoly as a market with a single seller, no close substitutes for the product, and high barriers to entry. Barriers include legal protections like patents, economies of scale, and ownership of necessary resources. A monopoly faces a downward-sloping demand curve and sets price above marginal cost to maximize profits where marginal revenue equals marginal cost. This results in lower output and higher prices than under perfect competition, reducing consumer surplus and creating deadweight loss.