As well as a passport, many countries require a visa to enter. This is simply a document or stamp issued by a country giving you permission to enter for a given period of time and for certain purposes, which is usually stamped or glued inside your passport, or issued as separate pieces of paper.
Here are some examples of entry requirements around the world (check with the country’s embassy or consulate before you leave, though):
New Zealand doesn’t require US or EU citizens to obtain a visa in advance but you do need a return or onward ticket (plus a visa for the country where you are heading, if required).
Some countries (for example, Australia) use electronic “visas” where you can apply online and, if successful, your name is added to a database which is checked when you enter the country.
Indonesia requires an onward ticket for entry but these can be bought cheaply after landing at the Indonesian airport and then sold later if not needed.
There are reciprocal arrangements between various countries, too, like the US Visa Waiver Program, which allows citizens of specific countries to travel to the US for tourism or business for up to 90 days without having to obtain a visa and vice-versa. The reciprocal arrangement means that most European countries will admit citizens of the United States with just a valid passport.
Canada just requires that US citizens have official identification (usually a driver’s licence), and sufficient funds to enter.
Mexico requires just an id to travel within 26 kilometers of the border, and a $15 visitor card beyond that (bought at checkpoints).
Thailand will issue a free transit visa valid for 15 days to those arriving there without a visa as long as you have an onward airline ticket. For $25, paid in advance at a Thai embassy or consulate, you can get 30, 60 or 90 day visas (valid from the date of entry), with no need for an onward ticket.
A visa for visiting India is multiple entry (you can leave and re-enter on the same visa), and can be obtained at your local Indian embassy. You will get an application form which you send back with your passport and the required fee by registered mail. Your passport is then returned with the visa inside. This will take about two weeks, although, for an additional fee, you can get next-day processing. The visa is valid from the date of issue, not from when you enter the country.
Other things to be aware of are such things as the fact that there are certain countries that will not let you enter if you have an Israeli entry stamp in your passport (or if you use an Israeli passport when entering). Luckily, you can make alternative arrangements, for example, by applying for a second passport if you travel frequently to Israel.
The World Travel Guide says this: “Tourists [visiting Israel and] continuing [on] to Arab countries, excluding Egypt and Jordan, are recommended to request that an Israeli stamp does not appear in their passport. The granting of such requests is at the discretion of the authorities.”
As with passports, applying for visas is another thing that can take time (for visas to enter some countries it can take months), so, again, check the requirements for the countries you are visiting well in advance of your trip (here, for example, on the World Travel Guide website).
Once in a country it can be possible get visa extensions but sometimes it is easier to leave the country and come back on a new visa.
Finally, it also pays to take extra passport-sized photos for any additional visas that you might need while travelling.
