Essays on environmental taxes, tax evasion and public goods supply in the presence of imperfect competition

Imperfect competition generally leads to a failure to reach Pareto efficiency. The welfare loss associated with this failure gives the government reasons to intervene in the economy through the use of taxes and subsidies in order to promote efficiency. This introduces a new dimension for the role of taxation, beyond the usual ones of raising revenue and welfare redistribution associated with economies under perfect competition. However, it is not a priori obvious how beneficial such intervention may be.; We present here three essays dealing with general equilibrium economies and the role of taxation under imperfect competition. These three economies share the fact that at least one of their industries operate under imperfect competition, but each is concerned with a particular problem which has been studied extensively under perfect competitive assumptions. In the first chapter we study the optimal provision of public goods financed by distortionary taxes when there is a monopolistic sector in the economy. In the chapter, we assume that another market failure is present in the economy through the existence of a production externality generated by the imperfectly competitive sector. The problem of interest is that of second-best taxation of externalities in the presence of imperfect competition. The last chapter assumes that all the firms in the economy, either perfectly or imperfectly competitive, have the opportunity of concealing a fraction of their sales in order to (illegally) reduce the amount paid in taxes. We reconsider the problem of optimal commodity taxation under tax evasion when some sectors of the economy are imperfectly competitive.