Barriers to entry and exit protect existing firms and allow them to maintain high profits. They include economies of scale, brand loyalty, and control of important technologies. Google faces few barriers to entry in search due to its vast scale and vertical integration advantages over potential competitors. Firms use strategies like limit pricing, predatory pricing, and brand proliferation to discourage competition. Industries with high minimum efficient scale and falling average costs are less contestable due to barriers to entry. Established firms have cost advantages from learning, integration, and scale that make entry difficult for competitors. Plant closures occur when price falls below average costs, showing the shutdown price.