The present research work, based on the Colombian tax law, focus on learning and understanding the “Principle of Favorability”, which is defined as the principle that removes the principle of non-retroactivity of the law, always that the new law gives legal benefits to the tax payer and the community; therefore, the Constitutional Court permits that the constitutional principle of non-retroactivity is not absolute and find valid exceptions to its implementation. The development of the “Principle of Favorability” is not found in the Constitution from 1886, it has only flourished in the shadow of the Constitution of 1991 because of the developments in the law of the Constitutional Court; pronouncements which have been subjected to fierce resistance on the part of the State Council, which has set opposing positions to those of the Constitutional Court. The “Principle of Favorability” was created in the legal judgment C-527 of 1996, which is considered the founding judgment in the field.