Hi Pat,
While Mexico's native currency is the Peso, most places you go accept the US dollar as currency. However, accepting the US Dollar without a currency conversion will mean you will be on the short-end of the exchange stick, sometimes by as much as 25%.
It's best to exchange your currency for the Peso, ensuring you get the most purchasing value out of your money. You can do this at travel agents here in England, or banks and hotels in Mexico. Look around for different rates.
If you have any other questions then please do not hesitate to email me.
Kind regards
Cheryl, your editor