Decentralizing tax powers to the sub-national governments of a federation may lead to theoretical collective benefits and costs. Belgium is a federation composed of three regions enjoying partial but ever increasing tax autonomy. Today, some politicians ask for new fiscal powers while others fear this extension. In that context, we propose a qualitative evaluation of the transfer of tax powers. We examine the benefits and costs of fiscal decentralization, using the criteria proposed by the theory. Therefore, we analyze how regional governments have made use of their fiscal powers. Each significant fiscal decision is classified according to the positive or negative expected collective effects. The objective is to get an overall view rather than a piecemeal one. Finally we draw some guidelines for the future of fiscal decentralization in Belgium and discuss how they are applicable in general in decentralizing countries.