This book, first published in 1984, examines the use of simple general equilibrium models in analysing the effects of taxes. The replacement of the earlier partial equilibrium approach has yielded numerous insights and conclusions, and these are examined here alongside the simple general equilibrium reasoning.

My dissertation examines theoretically the effects of environmental taxation on welfare in various cases. Using a general equilibrium model, the first chapter shows that a Pigouvian tax provides a larger welfare gain than an output tax, since it induces substitution among inputs as well as reduction in output of the dirty good, while an output tax induces only the output reduction. Using data for China and the U.S., numerical simulation results show that the potential welfare loss from not being able to use a Pigouvian tax is much larger in developing countries than in developed countries. The second chapter focuses on the fact that recycled material needs reprocessing to be substitutable for virgin material. Reprocessing uses resources and, in the process, generates pollution. Incorporating these 'imperfect' characteristics into a simple general equilibrium model, I examine how these realistic factors affect the structure of taxsubsidy schemes when the Pigouvian taxes are not available. A generalized Deposit-Refund system can achieve the optimum if illegal dumping is not taxable. Without a Pigouvian tax on illegal dumping, recycling is subsidized for its role in diverting illegal disposal into proper disposal. If Pigouvian taxes on neither illegal disposal nor waste from imperfect reprocessing are available, a combination of output tax on reprocessed material and subsidies for clean inputs can be used to restore the optimum. In the process, another reason to subsidize recycling emerges: recycling is a clean input for imperfect reprocessing. The third chapter focuses on the validity of the results obtained in the first chapter in the case of two vertically-separated oligopolies where the upstream industry is polluting. Using an analytical partial equilibrium model, I show that a tax on pollution is potentially superior to a tax on intermediate good, since the former can utilize both the upstream firms' input substitutability and the downstream firms' input substitutability, while a tax on intermediate good only utilizes the downstream firms' input substitutability. I also derive the conditions that government can improve social welfare through various revenue-neutral tax reforms.

"Income redistribution is one of the primary concerns for policy makers and economists. Among the countries in the Organization for Economic Co-operation and Development (OECD), the degree of income redistribution (measured by the percentage decrease in the income Gini coefficients between the before and after taxes/transfers) ranges from 5% (Chile) to 49% (Ireland). Understanding and comparing redistribution policies across countries in a unified framework is not an easy task. However, recent developments in quantitative general equilibrium heterogeneous-agents models allow us to address several issues. In this dissertation I study three issues about the redistribution polices using a state-of-the-art quantitative general equilibrium model. Chapter 1 uncovers Pareto weights that justify the current progressivity of income taxes in 32 OECD countries. Chapter 2 shows that the current tax rate in the U.S. can be close to political equilibrium under an ex-ante differences in earnings ability and income-dependent voting behaviors. Chapter 3 finds and explains the negative relationship between economic outlook and income redistribution. In Chapter 1, we develop a model that reproduces income distribution and redistribution policies in 32 OECD countries. The individual income tax schedule is assumed to follow a log-linear tax function, which is widely used in the literature (Heathcote et al., 2016). According to our model, the optimal tax progressivity under the equal-weight utilitarian social welfare function varies from 0.21 (South Korea) to 0.41 (Ireland), and the corresponding optimal redistribution ranges between 20% (South Korea) and 37% (Ireland). For 22 countries, mostly European countries, the current progressivity is higher than optimal. In the other 10 countries, including the U.S., the optimal progressivity is higher than the current one. In our model the optimal tax progressivity is favored by the majority of the population in almost all OECD countries. Then, why does the current (suboptimal) tax rate prevail? The society's choice for redistribution may differ from the equal-weight utilitarian welfare function (Weinzierl, 2014; Heathcote and Tsujiyama, 2016), or can be affected by various factors such as the externality of public expenditure (Heathcote et al., 2016), and the preference heterogeneity (Lockwood and Weinzierl, 2015). In this chapter we ask a rather simple positive question within the utilitarian framework: what are the weights in the social welfare function that justify the current tax progressivity as optimal? We interpret these relative weights in the social welfare function as broadly representing each society's preferences for redistribution and political arrangement. According to our calculations, in Sweden, the average Pareto weight on the richest 20% of the population is only 0.53, whereas that on the poorest 20% is 1.74. By contrast, in Chile, the Pareto weight on the richest 20% is 2.65, whereas that on the poorest 20% is a mere 0.15. In the U.S. that on the richest 20% is 1.45 and that on the poorest 20% is 0.60. We also compare our social weights to those from Lockwood and Weinzierl (2016), who extend Mirrleesian (1971) framework to uncover weights. To our knowledge, this is the first study that compares how societies aggregate individual preferences over redistributive policies, and does so across a large set of countries. The utilitarian social welfare function often predicts that the optimal income tax rate in the U.S. is much higher than the current rate (e.g., Piketty and Saez, 2013). In Chapter 2, we focus on the interaction of ex-ante heterogeneity in household earnings and income-dependent turnout rates. While the relationship between each factor and income redistribution has been reported by many studies (Benabou and Ok, 2001; Charite et al., 2015, Mahler, 2008), quantitatively neither effect alone is large enough to explain the current tax rate. However, the interaction of the two magnifies the effect on redistribution, political equilibrium can be close to the current tax rate. More specifically, we construct three model economies: no ex-ante heterogeneity (NH), small ex-ante heterogeneity (SH), and large ex-ante heterogeneity (LH). All three economies match the overall income dispersion (Gini coefficient) in the data, but the share of ex-ante productivity (ability) and ex-post productivity (shocks) is different. According to our estimates following Guvenen (2009), 31% (SH) and 57% (LH) of wage dispersions are driven by ex-ante productivity. In the NH, by design, all wage dispersions are from ex-post productivity. For tractability, a flat tax rate and a lump-sum transfer are assumed in this chapter. The current tax rates in the three economies are set to 24% from the U.S. data. According to our model, the optimal tax rates under an equal-weight utilitarian social welfare criterion are similar in all three economies: 37% (NH), 38% (SH) and 37%. These high optimal tax rates are consistent with a majority of literature based on a utilitarian social welfare function (e.g., Piketty and Saez, 2013; Heathcote and Tsujiyama, 2016). The tax rates chosen by a simple majority rule are 37% (NH), 37%(SH), and 34% (LH), still much higher than the current rate. However, once we introduce increasing voter turnout rates with income, as in the data (Mahler, 2008), the political equilibrium vastly differs across the three economies. The tax rates chosen by effective voting are 35% (NH), 33% (SH), and 27% (LH). In LH, where income dispersion is driven mainly by ex-ante productivity, the insurance benefit from a heavy tax-and-transfer policy diminishes, and high-ability households are more against strong redistribution. If their turnout rates are higher, a relatively low tax rate can become a political equilibrium, which is close to the current tax rate. In Chapter 3, I find a new relationship between the economic outlook and redistribution among 33 OECD countries between 1996 and 2010, using the historical forecasts in the World Economic Outlook and the Standardized World Income Inequality Database. A one percentage point decrease in expected growth is associated with a 0.005 point and 0.9% increase in the income Gini before taxes and transfers. To examine this relationship I introduce labor-augmenting technology into my model at the cost of assuming a simple tax structure (linear tax and lump-sum transfer). The current tax rate (21.8%) and labor-augmenting productivity growth (3%) are chosen to match the U.S. economy before the Great Recession. Then, after an unanticipated productivity slowdown, the productivity growth decreases to 1%. Once productivity slows down, households save more to prepare for lost consumption in the future. As the capital-to-output ratio increases, the interest rate goes down from 4% to 1.7%. As seen in previous chapters, explaining the current tax rate is still disputed. Leaving this question to other studies, this chapter focuses on the effect of a productivity slowdown. More specifically, social weights that justify the current tax rates are derived, and, given these weights, the optimal tax rate under the low-growth regime is calculated. While all households save more against productivity slowdown, poor households, who are close to borrowing constraints, have more difficulty in increasing their savings. Hence, higher tax rates (23.6%) and more transfers can enhance social welfare under the low-growth regime. This relationship between expected growth and redistribution is similar to my empirical estimates. A general equilibrium effect from increased capital plays an important role. If interest rates are fixed, private savings are more effective against a productivity slowdown, since households can continue to save at the same rate. In this economy the optimal tax rate under the low-growth regime is much lower than the current rate."--Pages v-viii.

The first essay studies the Marginal Cost of Funds in the existence of tax evasion. We develop a general equilibrium model of tax evasion, including the expected utility of taxpayers and three different revenue-raising government policies. In this rich model environment, we analytically derive the marginal cost of funds (MCF) for the alternative policy instruments. We consider two main fiscal reforms: the revision in the nonlinear tax scheme and the changes in enforcement mechanism (the audit and penalty rates). First, we derive the MCF for the tax reform and find its key determinants. The derived MCF is greater than the previous ones since it includes a "risk-bearing cost" as well as tax distortion. The reform in enforcement mechanism generates MCFs in different forms. Two more MCFs with respect to audit and penalty rates are presented. Finally, we compare these three different MCFs in numerical example and provide some policy implications. The second essay explores optimal tax structure in the presence of status effect. When the consumption of certain goods affects one's social status, this externality creates two opposite effects in a society. Seeking higher status through "positional goods" gives individuals much incentive to supply labor but still allocates income for less "nonpositional goods" as well. In this case, differential taxes on positional goods work as corrective instruments to internalize the social cost stemming from status seeking. Furthermore, the differential taxes generate revenue that can be used to alleviate preexisting income tax distortion. Thus, the differential taxes on positional goods could give so called "double dividend." I develop a game-theoretic model in which each individual with a different labor productivity unknown to the others engages in a status-seeking game, and the government has a revenue requirement. Then I show that, under a condition in which utility is separable between positional goods and leisure, a revenue-neutral shift in the tax mix away from nonlinear income taxes towards positional-good taxes enhances welfare. Hence, the differential taxes on positional goods are necessary together with the nonlinear income taxes for an optimal tax structure. The third essay explores the impact of increasing capital mobility on regional growth and environment. I develop an endogenous growth model in which each local government competes against the others, to induce imperfectly mobile stock of capital into its region. Then I show that an increase in capital mobility generates "tax importing" due to which each locality experiences a higher growth rate and more degraded environment. That is, the increasing mobility dampens the capital tax and transfers the burden of pollution abatement to the locality. This finding supports the hypothesis of "race to the bottom" in environmental standards. Identifying a reduction in overall welfare of residents, I consider two alternative federal interventions in the model: uniform environmental standard and requirement of lump sum transfer or tax. Both of these federal instruments enhance the residents' welfare.

This thesis is composed of three essays, and contributes to the literature on optimal design of tax and transfers schemes in heterogeneous agents general equilibrium models. In the first chapter, Redistributive Capital Taxation Revisited, coauthored with Ctirad Slavik and Hakki Yazici, we use a rich quantitative model with endogenous skill acquisition to show that capital-skill complementarity provides a quantitatively significant rationale to tax capital for redistributive governments. The optimal capital income tax rate is 67%, while it is 61% in an identically calibrated model without capital-skill complementarity. The skill premium falls from 1.9 to 1.84 along the transition following the optimal reform in the capital-skill complementarity model, implying substantial indirect redistribution from skilled to unskilled workers. These results show that a redistributive government should take into account capital-skill complementarity when taxing capital. In the second chapter, Optimal Taxation of Automation, I focus on the asymmetric effects of automation on labor markets. I provide a general equilibrium model that distinguishes between low-and high-skill automation to study optimal taxation of those technologies. Low-skill (high-skill) automation generates a downward pressure on low-skill (high-skill) wages. Modeling the two types of automation is important as both are empirically relevant, and each has a different impact on wages of workers with different skill types. I calibrate the model to the US economy along several dimensions, and find that for a given level of technology, it is optimal to distort automation adoption in order to compress wage inequality and increase labor share of income to provide redistribution. In particular, it is optimal to tax low-skill automation while subsidize high-skill automation when the transitional dynamics are taken into account. As a result, consumption inequality and both before and after-tax income inequality decline and labor share of income increases relative to status-quo over transition. In the third chapter, On the Implications of Unemployment Insurance and Universal Basic Income in a Frictional Labor Market, I revisit the efficiency and equality considerations regarding the optimal provision of unemployment insurance (UI) benefits when workers' outside options vary substantially. The chapter aims to make comparisons between UI and universal basic income (UBI) policies to investigate whether UBI could be a tool to improve workers' hand in the wage setting and how transfers to unemployed -UI or UBI - and taxes impact the wage setting outcome across income distribution.