I am a Mexican citizen with a visa that expires May 31, 2015. I need to enter the US for five days in the last week of January.
Can I do so or do I need to renew it before entering the US?
US visa validity works differently than in most other countries.
In the US, the visa validity dates are the dates in which you may travel to a port of entry to enter the country. Your duration of stay may extend beyond the visa expiration, up to the limits for your visa type.
At the time you enter, the border guard will stamp or write in your passport with the date that you must depart the country. Be sure to check that this date is correct before you leave the border checkpoint.
(Public domain image provided by US Embassy Philippines)
You can use it to enter the U.S. on May 31, 2015, or any day before that.