Thesis: In this dissertation, I study the implications of policies with heterogeneous sectoral impacts in three separate research fields of macroeconomics: (i) environmental policy, (ii) foreign aid and (iii) the political economy of the twin deficits. Through the three chapters of this thesis, it is argued that, in all these three contexts, the sectoral impacts of policies play important roles in the policy evaluation and in the determination of optimal policy. In the first chapter, the policy of concern is the pollution tax. The paper provides a theoretical model to explain why in top income percentiles, there can be a negative relationship between household's income and their support for pollution tax. In the second chapter, I study the macroeconomic impacts of foreign aid and I consider two sectors: tradable sector (T-sector) and non-tradable sector (N-sector). I consider two forms of foreign aid: (i) aid which is transferred to the households and (ii) aid which is used to finance public investment. I investigate the impact of the liberalization of capital market on the optimal form and on the performance of foreign aid. In the third chapter, I consider the same sectors as in the second chapter : T-sector and N-sector. The focus of this chapter is rather on the political economy of the twin deficits: a deficit in current account induced by a deficit in fiscal balance. Econometric analysis of the paper finds evidence that wage centralization, in a cross-section of industrialized economies, is significantly associated with lower deficits in current account and budget balance. The paper provides a political economy framework to explain this empirical finding.