Despite being one of the largest cities in the world, with a population of some 20 million, São Paulo has a quite small metro system, when compared to its European or North American counterparts.

As of 2004, it consists of four lines: Line 1, Line 2, Line 3 and Line 5-Lilac, serving a total of 55 stations. The metro system carries 2,500,000 persons a day. Another company, CPTM (Companhia Paulista de Trens Metropolitanos) runs railways converted into metro, which total six lines (A,B,C,D,E,F), about 250 km, some 92 stations. Metro and CPTM have integration between the stations.

The first line, Norte-Sul (North-South), later renamed Linha Azul, and then Linha 1 – Azul, started operations on September 14, 1974. That was after an eight-year gestation period that started in 1966, under Mayor Faria Lima .

Expansion on the metro includes new lines. In late 2004 work will start on a USD $1 billion 12 km all-underground line, Linha 4 – Amarela, with ten stations, transporting almost a million people a day. Currently (2004) line 2 is being expanded, with the first two new stations due to open by 2006. Line 5 will be expanded by some 10 km underground. An 10 km airport express line is in the short-term plans also. The plans also include revamping the CPTM heavy rail system, which will add several million passengers into the system. It is expected that the São Paulo Metro and CPTM systems will carry some 7 million people on average week days by 2012, as opposed to today's 4 million (Metro: 2.5 million; CPTM: 1.5 million as of 2004).

Both Metro and CPTM operate as a government company, and have received some prizes in the recent past as the cleanest metro system in the World.