This paper deals with the restoration work accomplished on the architectural elements of the Templo Mayor, the mural paintings, the sculptures, and the various metal, stone, and organic materials found in ritual deposits. Soils, humidity, temperature, light, biological damage, wind, seismic movements, and human activity are the environmental conditions that are studied for impact on the site. The choice of conservation treatments was based on the relative degree of deterioration of the materials. Stonework, stucco, and sculptures received appropriate treatments as reported in representative cases. The treatments of objects in offerings began in situ, and was preventive in nature.