Social security in Mexico has gone through three phases during the twentieth century and early twenty-first: social security, social security, social protection -as has happened in other economies of the international context-. Currently, this system faces strong challenges in the face of a demographic change with a tendency of the young population that diminishes in the face of a growth of the adult population that will accelerate in the next decades. This situation is not exclusive to Mexico, but a situation that the world is going through during the present century. This situation requires the establishment of measures to make the social security system sustainable. This article addresses social security in Mexico and its transition to social protection, which, although it has made progress, faces problems in terms of coverage, sustainability, quality, efficiency, as well as the need to incorporate an important segment of occupied population that is in informality.