There are several barriers that can prevent firms from entering or leaving markets. Barriers to entry include economies of scale, brand loyalty, control of important technologies, expertise and reputation. Strategic entry deterrence by existing firms includes hostile takeovers, product differentiation, capacity expansions, and predatory pricing. Patents provide monopoly power but can also stifle competition. Innovation is both a barrier, through property rights, and an enabler, by reducing barriers. Process innovation lowers costs. Established firms have cost advantages from learning, integration, customer retention, and monopsony power. Legal barriers include licenses, patents, franchises, and import controls.