An Electronic Travel Authorization (eTA) is generally required for visa-exempt foreign nationals flying to or transiting through countries like Canada or Australia. For Canada, this includes citizens from countries like the UK, France, Germany, and Japan who do not need a full visitor visa. Notably, U.S. citizens do not need an eTA to enter Canada, but U.S. Green Card holders (permanent residents) do need to present their Green Card and a valid passport. The eTA is only required for travel by air; if you enter Canada by land (car or bus) or sea (cruise ship), you typically do not need one. The authorization is linked digitally to your passport and usually lasts for five years or until the passport expires. It is essential to apply through official government portals to avoid the inflated fees charged by third-party "processing" sites.