This dissertation develops three independent yet related frameworks to identify economic mechanisms through which financial frictions affect the aggregate economy over the business cycle and along the path of economic development. There are three chapters in this dissertation. In each chapter, a theoretical model is constructed based on motivating empirical facts, followed by quantitative analyses disciplined and evaluated by data at both the macro- and micro-level. Chapter 1, Financial Frictions and Agricultural Productivity Differences, explores the role of financial frictions in accounting for agricultural employment share and labor productivity differences across provinces in China. A two-sector general equilibrium model with a subsistence consumption requirement and financial frictions is constructed. Limited credit decreases the use of intermediate inputs and increases the use of labor input. As a consequence, workers are trapped in the agricultural sector and agricultural labor productivity is low. Since agricultural employment consists of a large percentage of total employment, aggregate labor productivity is also low. Quantitatively, financial frictions alone explain more than 25% of the observed employment share and productivity differences. Financial frictions amplify the effect of TFP differences on agricultural productivity differences by 30%. Cross-country sectoral value-added per worker differences are large. Value-added per worker is much higher in non-agriculture than in agriculture in the typical country, and particularly so in poor countries. Even though these agricultural productivity gaps (APG) are large, poor countries devote most of their employment to agriculture. Based on a novel data set of value-added at the sectoral level that is comparable across provinces, I find the same patterns across provinces in China. In the second chapter, Credit Constraints, Human Capital and the Agricultural Productivity Gaps, I explore and quantify the role of financial frictions in accounting for these puzzling patterns. A two-sector heterogeneous-agent model with human capital investment, occupational choices and financial frictions is developed. Financial frictions depress human capital accumulation and distort occupational choices of rural households. Quantitatively, our model could account for a substantial portion of the observed cross-province differences in sectoral productivities and the APGs. The financial friction alone could account for 80% of the across-province differences in AGPs. It also explains 1/3 of the sectoral productivity differences and 1/5 of the differences in the agricultural employment share and the aggregate productivity across provinces. In Chapter 3, A Search-Theoretic Model of Capital Reallocation, I investigate how search frictions in the capital market affects capital reallocation across firms and the price of used capital over the business cycles. A tractable dynamic general equilibrium model is developed to account for procyclicality of capital reallocation. Firms are heterogeneous in their productivities and they trade used capital in a market which is subject to search frictions. After idiosyncratic productivity shocks are realized, firms are able to adjust their capital stock to a more favorable level before production. In the booms, the demand of used capital increases and the market tightness of used capital market is small. Hence, capital reallocation is larger and the price of used capital is higher. During the recessions, buyers demand less used capital and the market tightness is large. Consequently, capital reallocation is smaller and the price of used capital is lower. Quantitatively, the model could generate a correlation coefficient between capital reallocation and output that is consistent with the data.