Construction of Mexico City's subway system began in 1968. At that time, the nature of the Mexico City subsoil, as well as aggressive regional settlements and seismicity conditions, posed serious challenges to the project. Despite the obstacles, to date more than 150 km of subway line have been constructed. The first lines were constructed using the underground, open caisson method; later lines were built overhead, in tunnel (successfully using the NATM), and on the surface. In some cases, excavations down to more than 15 m depth were executed close to buildings of significant historical and architectural value. To accomplish this, accurate construction procedures were used to cross the existing lines without discontinuing their operation at any time. This paper summarizes these experiences and offers some reflections on the future of underground excavations in Mexico's capital city for uses such as parking lots and commercial passageways.