To travel internationally, you will need a passport issued by your government. It is your proof of your citizenship. It is your most valuable possession when traveling. You will need to present it at most international border crossings, to various officials, and to hotels.
A passport has your photo, name, birth date, and birth location (state in the U.S.). It also contains the passport number, place of issue, and expiration date. You will be copying all of this information onto forms repeatedly when entering and leaving countries.
The remainder of the passport is comprised of blank pages for visas and stamps. Many countries require a visa for entry (see below), so these pages will gradually fill up with use. The normal passport should suffice for tourist travel, but if you travel heavily then you can request a thicker passport with extra pages. You can also request additional pages added onto an existing passport, if necessary.
United States passports are good for ten years. However, most countries refuse to issue visas or permit entry on passports that are within six months of their expiration dates. So as soon as your passport reaches nine years, it’s time to start thinking about renewal. Since all your hard-earned visas will not be in your new passport, it is a good idea to think strategically about renewals if you’re coming down to the last few years and you anticipate getting a difficult visa.