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 leftwinger 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.
When he becomes president in December, Mr Pena Nieto will have to face the escalating violence of the drugs war in the northern states.
He has pledged no return to the PRI's pre-2000 policy of tolerating drug cartels in return for civil peace, and has announced plans to establish a special paramilitary police force to fight the drug barons alongside a stronger army presence.
The first major success of this change in policy came with the resst in July 2013 of Miguel Angel Trevino Morales, the head of the brutal Zetas cartel, wanted in both Mexico and the United States for ordering massacres and trafficking on a global scale.