Do all countries require a passport for entry or only certain ones?

Most countries require a passport to enter, but there are a few that don't require a passport but instead require other forms of documentation, such as ¹: - Valid permanent resident card or permanent resident travel document for Canadian permanent residents - Valid U.S. passport, green card or equivalent valid proof of status in the United States for lawful permanent residents of the U.S. - eTA to board the flight to Canada for visa-exempt travelers - Visas to come to Canada by any method of travel for visa-required travelers Additionally, some countries require passports to be valid for a set period, usually three or six months, before and/or after a visitor's arrival date ² ³.