There are a few words where English and American spelling and punctuation differ.
The most important of these are as follows:

  • English words ending -our correspond to American words ending –or:
    examples: English ‘neighbour’, ‘neighbourhood’ and ‘colour’ = American ‘neighbor’, ‘neighborhood’ and ‘color’.
  • 2. English words with a double ell become a single ell in American:
     examples: English ‘labelled’, ‘modelled’, ‘modelling’ = American ‘labeled’, ‘modeled’, ‘modeling’.
  • Some English words ending –re correspond to American words ending –er:
    example: English ‘centre’ = American ‘center’.
  • The English word ‘disc’ (as in ‘open disc’) = the American word ‘disk’.
  • The English word ‘programme’ = the American word ‘program’ (except for a computer program, where the American spelling is universally used).
  • The English distinguish between the verb ‘practise’ and the noun ‘practice’; the Americans spell both ‘practice’.
  • The English use ‘defence’; the Americans use ‘defense’.
  • Some words are different: in English, certain groups are ‘soluble’; in American they are ‘solvable’.
  • Punctuation differs, as in the ‘American comma’ for lists of three words or phrases:
    English ‘Tom, Dick and Harry’ = American ‘Tom, Dick, and Harry’.
    For quotations, the English put the punctuation outside the quotation (when it is not part of the quotation), whereas the Americans (wrongly) put it inside’: for example,
    English, ‘To be or not to be’, from Hamlet, is a well-known quotation.
    American, ‘To be or not to be,’ from Hamlet, is a well-known quotation.   

(by Robin Wilson, UK)