Changes

U.S. and Canadian citizens are NOT required to show a passport. At least not yet. That doesn't mean a border guard won't ask to see one, though. But, a border guard is not supposed to deny you just because you don't have a passport. Until January of 2008, border guards are supposed to accept continue accepting "oral declarations of citizenship" which basically means, "you have to believe me because I told you so."

If you are a U.S. citizen going into Canada or a Canadian going into the U.S., they have the right to a guard can deny you entry for a number of reasons (usually because of a criminal record or you don't look like you have enough money for lunch at a fast-food restaurant). But don't think that just 'cause you don't own a passport you can't cross. You can.