British English and American English differ in a number of spellings, as can be seen in the following examples:

Generally American English or as a word ending is equivalent to our in British English, American er as a word ending is sometimes equivalent to re in British English.

In American English the final -e is removed from verbs before adding ing; in correct British English this is not done giving routeing (British) and routing (American); however, the American practice of dropping -e is becoming quite common in British English.

American English tends to prefer ize and ization whereas British English prefers ise and isation contrary to statements by certain well known British authorities.

Canadian spelling seems to be intermediate between the British and American (US) forms but is generally closer to British practice. Also, there are widespread regional variations in both Canada and the US.

There are, of course, exceptions to the above rules. American usage is glamour, not glamor, and advertising, not advertizing. British usage has honorary and honorific without the "u". Sometimes the British usages centre and theatre are used in the US, particularly where the establishment in question wants to suggest that it is of superior quality.

[Adapted from Burden, Peter. "WWlib Notes on American English.". 25 Feb. 2001.]