The book consists of three parts. The first part analyzes the stock market dynamic under the presence of agents with heterogeneous beliefs and connects it to commonly observed asset overvaluation. Its two main results are that the long-run equilibrium price is the risk-neutral fundamental price even though all agents are risk-averse and that heterogeneity of beliefs persists. The second chapter describes the interactions between a borrower and creditors, where the borrower has private information, and the loan sizes are determined endogenously by the competitive credit market. It is shown that without behaviorally honest types all equilibria but one are inefficient and result in the country’s eventual default. The result helps to explain why developing countries often fail to establish a good reputation in order to attract potential investors. The third chapter experimentally analyzes the importance of utility and action interdependence in subjects’ reasoning. The results show that such recent theories as fairness, altruism, reciprocation, etc. have a rather modest effect and explain less than half of subjects’ deviation from payoff-maximizing behavior.