This paper assesses the current Colombian mining tax and royalty regime in terms of efficiency, competitiveness and revenue performance vis-a-vis other relevant mining countries. It then discusses the convenience of introducing a Resource Rent Tax (RRT) to new mining projects (together with a reduced common royalty rate for all minerals) and simulates its potential effects on efficiency and revenue performance. In particular, the paper examines the interactions between a RRT, royalties and the Corporate Income Tax under different RRT designs, tax rates and capital return allowances. It also discusses the convenience of project by project against sectorial ring-fencing. It concludes with a blueprint for reform as well as political economy and administrative considerations for the specific case of Colombia.