The main difference is that British English keeps the spelling of words it has absorbed from other languages, mainly French and German. Whilst American English spellings are based mostly on how the word sounds when it is spoken.

UK and US spelling differs in several areas. Generally speaking, British English has retained more of the spelling of words originating from other languages (e.g. French, Greek, and Latin) whereas American English has adopted spelling that more closely reflects how the word is pronounced.

In general, American English tends to have slightly stricter rules (at least for formal writing). British English is a bit more flexible on points like spelling (e.g., -ise vs. -ize) and punctuation (e.g., quotation marks, placement of commas).

A majority of the spelling differences between American and British English fall into the following categories: Latin-derived spellings - our (British) and - or (American). e.g. colour vs color - re (British) and - er (American). e.g. centre vs center - ce (British) and - se (American). e.g. defence vs defense