With the intensification of the constraints on government finances caused by the crisis, tax avoidance has become an important stake of public policies. Public economics of taxation fails to integrate the dimensions of avoidance in the search for optimal taxation. In fact the purely microeconomic foundations of optimal taxation do not allow the integration of the coercive dimension of taxation, the study of all the costs due to taxation and a correct representation of behaviors in the case of tax evasion. New developments founded on new hypothesis permit new generation of researches to emerge and lead to a set of recommendations in the field of anti-fraud tax policy. Nevertheless in the case of firm avoidance, especially transnational companies with many subsidiaries, the progress are weak.