As an American living in France, one difference that I really notice is politeness. In the US, people are casually friendly, but not always polite. In France,

As an American living in France, one difference that I really notice is politeness. In the US, people are casually friendly, but not always polite. In France, politeness manifests as respectful words and actions, consistently. It doesn't hurt that formal politeness is part of the French culture. It's 'hi, how are you?' vs 'good day, sir', because most of the time the 'how are you' is not really a question, but an expression of friendliness. There is also a fairly clear boundary between acquaintances, friends, and 'BFFs' in France. That boundary is not always clear in the US. It's not as formal as in Germany, where there is a sort of ceremony when two people want to recognize a stronger friendship. In France people (in my social circle, anyway) just switch from formal ('vous') to familiar ('tu'). I've been told that some people have a little discussion about it before switching, but I've never seen that.