In the US, your passport must be valid and NOT TO EXPIRE WITHIN 6 MONTHS or you will not be allowed into some countries, even if it's close, like two days, which happened to friends of mine. Everything was OK at the USA airport, BUT when transferring in Japan on the way to Indonesia, they weren't allowed to continue to their scuba vacation resort. Now that is a hard lesson. Research each country you plan to visit, or even LAYOVER, and double-check the expiration date and each countries requirements.
Also, there is a blank page rule for your passport. What? You must have a certain number of blank pages in the back of your passport for them to stamp. Again, there is no negotiating, so find out up front. Or at least have 6 blank pages available. Yup, frustrating to say the least. Google is your friend in these matters.
Also as of 2026, new digital requirements are becoming the norm. EES uses facial recognition and fingerprints to track you digitally. Passport requirements change daily, so it's best to read up before you go.
One last FYI, ID theft is getting easier through RF scanners that access the chip embedded in your passport, drivers license and credit cards. This mainly happens in airports. Check En Route Travelware's RFID blocking sleeves, moneybelts and document holders that will keep your information confidential.