Visitors to Belize MUST have a passport that is valid for the length of your stay. While the passport validity must last until at least 3 months after your return journey, it is advisable to ensure that the passport is valid for at least an additional 6 months from your departure date. You also need to have a return ticket and enough money to last throughout your stay (BZD 120, USD 60).
Belize Tourist Card
The simplest method for spending time in Belize is the Belize Tourist Card. You simply get a stamp in your passport, that allows you to spend a month enjoying Belize. After (or within) that month, you can leave at any time. However, should you choose to extend your stay in Belize, you can ask an Belize immigration officer to extend your belize tourist card for you.
Note that you are not allowed to work when you enter Belize on the Tourist Card!
For more information, please check out the Belize Tourism Board website at http://www.travelbelize.org/