Remember the time when the world was practically at your doorstep? Well, it still is, but you'll need to make sure that you have something to show for when you get back from that long-planned Caribbean cruise, or that spring break vacation in Cancun.

The world hasn't shrunk in any way post 9/11, but the U.S. Department of Homeland Security is making sure that national borders remain safe otherwise. If you're a frequent traveler, you're probably used to the erratic changes in exit-entry requirements between U.S. and foreign borders; but just in case you're not one of the 26% percent of all Americans who do not possess a passport, it's best to apply for one now, before packing that surfboard and sunscreen.

The US Department of State has recently enforced the Western Hemisphere Travel Initiative, which requires everyone who travels by air outside of US territory to present a passport upon re-entry. This initiative covers previous 'passport-free' roaming territories like Mexico and Canada.

The WHTI will not be implemented on land and sea travel until June 1, 2009, so you can still come and go between passport-free territories, without worrying if you'll be allowed to re-enter the United States without a passport. You don't need a passport to enter Mexico; presenting two valid IDs will be enough, such as your birth or naturalization certificate and driver's license. But you do need a passport to re-enter the US, especially if you're traveling by air.

Children and minors would need to present a certified copy of their birth certificate in particular, and if they are unaccompanied by their parents, would need to produce a notarized letter of consent for travel. Single parents who travel with their child need to present documents to support for legal custody, or a notarized letter of authorization to travel from the other parent.

The countries in the Caribbean region differ in entry requirements. Puerto Rico and the US Virgin Islands are basically part of US territory, and you can enter them without a passport. But if you're traveling to the British Virgin Islands, you'll need one to re-enter the US Virgin Islands. All of the other Caribbean destinations will usually require you to present a passport for entry, and even if they don't, you'll still need one to re-enter the US. The passport requirements also differ between places in the South Pacific and the Americas, but regardless of whether you need it for entry or not, you'll still have to present a passport when re-entering the US. Certain places are essentially part of US territory, such as the American Samoa, and crossing over to them is very much like crossing US state borders.

A cheaper passport alternative has already been approved for application since February 1st. The People Access Security Service Card is available for all passport-eligible citizens, for a very affordable price of 45 dollars. If you're a student traveler or a tourist on a budget, this can mean big savings, compared to the 97-dollar regular passports. Remember that passport and visa requirements differ between countries, as well as the allowable duration of stay; it is best to know each country's entry requirements in order to avoid the hold-up at the airport.