The focus of my research is dynamic political economy in macroeconomics. The first chapter of my dissertation studies the fact that Countries in the Organization of Economic Co-operation and Development (OECD) vary widely in their ratio of capital tax rates to labor tax rates. This chapter’s motivation is the strong negative correlation between the capital/labor tax ratio and old dependency ratio (defined as the ratio of population older than 65 years old to population between 20 and 65 years old) among 21 OECD countries. I study a parsimonious overlapping generations (OLG) majority voting model. In equilibrium, the retired households and relatively old working households hold a large amount of capital and vote for a low capital tax rate (implying a high labor tax rate), while relatively young working households hold a small amount of capital and vote for a high capital tax rate (implying a low labor tax rate). As a result, the model implies that countries with more old people have relatively lower capital taxes. The model takes the old dependency ratio as given and delivers a capital/labor tax ratio chosen by the median voter. The calibrated model presented here can generate not only this negative correlation, but also the tax ratios for the 21 OECD countries studied. In the second chapter, I extend the first chapter and study the Japanese economy and taxation for the past three decades. Population aging is a serious social issue in Japan. This chapter also shows that demographics is an important variable to explain the time series data of capital and labor tax rates. Interestingly, the model predicts that a benevolent or utilitarian government would set a capital tax rate to be zero as in many standard tax models. This result emphasizes the importance of modeling a political economy, as opposed to a standard social planning economy that has been extensively used previously. Finally, the third chapter focuses on US immigration policy. Illegal immigration from Mexico to the United States has been a hot topic to academic researchers and policy makers. This study quantitatively investigates the welfare effects of illegal immigration to native households in the US. More specifically, I simulate the model economy when the government deports every illegal immigrant. The simulation shows that the social welfare increases by 0.01 percent on average, and the poorest households’ welfare increases by 0.1%. Although, initially, there is a decrease in the interest rate and the unemployment rate as well as an increase in the wage, these variables in the no-illegal-immigrant steady state are almost identical to the initial steady state which is calibrated to the US economy.