The Prime Minister will meet with the Mexican president today and trade will be top of the agenda.
John Key is on a 10-day tour of Latin America, and says New Zealand needs to be more involved in one of the fastest-growing regions in the world.
Ms Key and his wife, Bronagh, will be visiting the presidential castle in Mexico City, and will be welcomed with a full military guard of honour. Mr Key is the first foreign leader to meet the new Mexican president, Enrique Pena Nieto.
Mr Nieto is embroiled in a number of controversies, including the head of the teachers' union allegedly embezzling $200 million.
Mr Key and Mr Nieto are likely to talk about the TPPA, a controversial free trade agreement involving New Zealand, the US and a number of other countries.