A passport is an essential document when traveling abroad. It is your ticket in and out of every country in the world. Lose it and you lose the ability to come and go as you please. You probably won't even be allowed to get on the airplane without it.
If you've already got a passport, make sure that it is still valid. You also have to ensure that your passport isn't going to expire while you are away. If it is near expiry, or you don't even have one, leave yourself plenty of time to go through the application process as it can often take quite a while. Keep in mind that some countries will not accept your passport if it will expire within six months of entering their country. And, make sure that their are enough empty pages for stamps and visas.
Although the process of applying for a passport varies from country to country the general requirements are the same. You will need your birth certificate or other official form of identification, photo identification, an application form and a couple of passport-size photos. You will also need to pay for your passport, which may cost any where from $30 to $100. When you are getting your photos taken, get four of five and keep the extras to take with you for visas and any other uses.
While traveling, the most important thing you must do is keep your passport with you at all times, including when you sleep and shower (these are times when it is likely to be stolen). Besides being extremely important to you, a passport may be a valuable commodity to foreigners. It can be sold for hundreds or even thousands of dollars. TREAT YOUR PASSPORT LIKE MONEY!
Getting your passport stolen is not your only concern. If you are stopped in a foreign country and can't prove you citizenship,you may run into problems or delays. Carry your passport with you at all times in case you are asked for identification. And don't give your passport to anyone. Some people claim to be 'officials' who need to verify your ID.
One interesting consideration is the order of the countries you will be traveling in. In the Middle East, there are so many countries in conflict right now that if they see an enemy's stamp on your passport, they may deny you entry into their country. For this reason, some travelers get TWO passports. However, check with your passport office about this option.
Before you leave, photocopy the main page of your passport (the one with your picture on it) so that if you do lose it then you will have a back-up copy to ease your troubles and speed up the process of getting a new one. Information you should have copied include: your picture, your passport number, identifying information and visa stamps. I usually get two photocopies of the important pages and give one to my travelling companion. If your bag gets stolen (or doesn't arrive in the country when you do), this will help you out. Don't keep the photocopy with your passport but instead keep it in another bag (like your traveling companions bag).
Also before you leave, scan your passport and e-mail it to your own e-mail address. That way, if you lose your passport, you will have a copy that you can access and print out from any internet caf�. This also works for health insurance forms, credit card information, phone numbers and addresses, and any other paperwork as well.
If you do lose your passport, or it gets stolen, notify the local police and your embassy or consulate immediately. Make sure you have your photocopies and identification with you when you report the loss. Any visa stamps in the passport will be lost so you will need new ones if necessary.
I also take a couple passport photos with me when traveling. If you need to get a visa to get into another country, you will usually need to get one of these pictures taken. Instead of hunting all over the city looking for a photo booth or photography store (or paying lots of money), you will already have the photos. I spent half a day in Israel getting a passport photo taken for an Egyptian entrance visa when it could have taken half an hour.
You can get more information on all passports at The US State Department, and if you're American, you can even apply for one on-line.