President: Enrique Pena Nieto
The rejuvenated Institutional Revolutionary Party returned to power in 2012 with a clear win in presidential elections by Enrique Pena Nieto.
He beat veteran left-winger Andres Manuel Lopez Obrador, and drove Josefina Vazquez Mota of the rightwing National Action Party (PAN) into a distant third place. This ended 12 years of PAN rule.
Born in 1966, Mr Pena Nieto began his political career in his twenties, working for the PRI and in the local government system in Mexico State, the country's most populous state, rising to win the gubernatorial election in 2005.
He won praise for his expansion of the transport and healthcare system and careful financial management during his six years as governor of Mexico State, which helped win him the PRI presidential nomination and the election itself.
Mr Pena Nieto faces escalating violence in the northern states' drug wars. Having pledged no return to the PRI's pre-2000 policy of tolerating drug cartels in return for civil peace, he has taken steps to deal with drug-funded corruption in local police forces.