Book excerpt: Heterogeneous agents models have become the norm in modern macroeconomics as the limitations of the representative-agent paradigm and the importance of studying household heterogeneity grow in recognition. Agent heterogeneity may not only be important to accurately capture the description of an aggregate equilibrium. Also, the representative agent assumption may hide many distributional effects and therefore could change the answer to many normative questions usually given by representative agent models.This dissertation contains three chapters exemplifying ways in which the consideration of heterogeneous agents in the modelling of macroeconomic phenomena has important repercussions for the predictions of the model and its normative implications. Chapters 1 and 2 show the importance of accounting for worker heterogeneity in the analysis of labor markets. Chapter 1 presents a search and matching model of unemployment with heterogeneous workers which's main features, are ex-ante worker heterogeneity and undirected search. These features enable the model to replicate the empirical correlations between labor market outcomes and proxy variables for worker productivity. The model displays job rationing, which makes it useful to understand the high levels of unemployment observed in deep recessions. It also constitutes a versatile tool for the analysis of several labor-market aspects in which worker heterogeneity could play an important role, such as the impact of employment policies that are believed to have asymmetric effects across the labor force.Chapter 2 provides an example of such applications by analyzing the effects of increments of a minimum wage. It explores theoretically and empirically the notion that minimum wages affect low-skill workers asymmetrically due to productivity differences. Using the model presented in chapter 1, with the incorporation of endogenous search intensity to account for the effects that minimum wages could have on worker participation, I show that a rising minimum wage lowers the employment and labor force participation of low-productivity workers by pricing them out of the market, while it increases the employment, participation, and wages of more productive workers that remain hirable. Chapter 2 also contains an empirical analysis that investigates and ultimately validates the model's predictions of changes in the minimum wage. Within the labor market for low-education (high school or lower) workers, increments in the minimum wage have diametrically opposed effects: they reduce the employment and labor force participation of teenagers with less than high school education, while increasing the employment and labor force participation of mature workers with high school educational attainment. A calibrated version of the model targeting the low-education labor market shows that, despite its opposite effects across the labor force, an increase in the minimum wage negatively impacts aggregate employment, labor force participation, and social welfare.Chapter 3 investigates the existence of complex dynamics in the behavior of exchange rates due heterogeneity in the expectations of their future value. A simple model of exchange rate dynamics featuring traders with heterogeneous expectations is introduced. The model is based on the asset pricing model in Brock and Hommes (1998) and features the BNN dynamic presented in Brown et al. (1950), a dynamic with desirable properties absent in other dynamics used in the literature. The chapter shows that even this simple model can easily generate complex and even chaotic dynamics in the exchange rate because of the interaction of traders with different beliefs. An important implication is that long-term exchange rate prediction is, in theory, difficult.