"This thesis extends the macroeconomic theory with heterogeneous agents by taking account of heterogeneous households' interaction among themselves, in the form of comparing their consumptions or incomes, and by allowing heterogeneous firms to interact in a strategic fashion. In Chapter 2, I study how behavioral hypotheses such as the concern for status (relative consumption) and inequality aversion can lead to useful predictions about the evolution of wealth distribution and asset accumulation. Households are heterogeneous in terms of initial endowments and idiosyncratic shocks to their labor productivity. I propose a generalized concept of consumption externalities which include as special cases the concern for relative consumption, and preferences that display inequality aversion. In Chapter 3, I focus on interactions among heterogeneous firms in an oligopolistic framework. I assume that that the products offered by these firms are not perfect substitutes. More important, the degree of substitutability may vary across products within the industry. I offer a general formulation of industry structure such that monopoly, oligopoly, and monopolistic competition can be obtained as special cases. In Chapter 4, we study how preferences that display ambiguity aversion play a role in the job search process and affects the equilibrium rates of unemployment and vacancy. Ambiguity refers to the lack of information about probability distributions. The traditional job search model assumes that there are random matches between job seekers and firms (or vacancies), and the random draws have objective probability distributions that are known to both sides of the markets. We modify this model and assume that economic agents are uncertain about the underlying probability distributions. This chapter contributes to our understanding of how ambiguity aversion affects the unemployment rate and aggregate productivity." --

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