In this dissertation, I study the implications of taxation -and other regulations- in environments with financial frictions and firm entry. The first chapter asks if there is a role for the regulation of the market of funds for firms that lack collateral and have a large uncertainty about their ability to generate profits. To answer the question, it characterizes optimal financial contracts in a competitive environment with risk, adverse selection, and limited liability. In this environment, competition among financial intermediaries always forces them to fund projects with negative expected returns both from a private and from a social perspective. Intermediaries use steep payoff schedules to screen entrepreneurs, but limited liability imp...