The Dissertation consists of three chapters. The first chapter is about bankruptcy. I set up a heterogeneous agents model to analyze the effect of bankruptcy on the credit market, entrepreneurship, growth and social welfare. First, lenient bankruptcy (e.g. small bankruptcy cost, less financial restriction for bankruptcy filers) decreases credit supply by increasing financial intermediaries\u27 loss. This results in the rise of the market interest rate. Second, lenient bankruptcy has a positive effect on entrepreneurship in general. It enhances the incentive for individuals to establish firms and easily shut down their firms. Therefore the share of entrepreneurs can be either smaller or larger since it is affected by these entry and exit rat...