There are several areas in which British and American spelling are different. The differences often come about because British English has tended to keep the spelling of words it has absorbed from other languages (e.g. French), while American English has adapted the spelling to reflect the way that the words actually sound when they're spoken.

If you're writing for British readers, you should only use British spellings. In one or two cases, the preferred American spellings are acceptable in British English as well, especially the -ize/-ization endings. While you can use both the -ise/-isation or the -ize/ization endings in British English, it's important to stick to one style or the other throughout the same piece of writing.

Here are the main ways in which British and American spelling are different.

Words ending in –re

British English words that end in -re often end in -er in American English:

British US
centre center
fibre fiber
litre liter
theatre theater or theatre

Words ending in –our

British English words ending in -our usually end in -or in American English:

British US
colour color
flavour flavor
humour humor
labour labor

Words ending in -ize or –ise

Verbs in British English that can be spelled with either -ize or -ise at the end are always spelled with -ize at the end in American English:

British US
apologize or apologise apologize
organize or organise organize
recognize or recognise recognize

Words ending in –yse

Verbs in British English that end in -yse are always spelled -yze in American English:

British US
analyse analyze
breathalyse breathalyze
paralyse paralyze

Words ending in a vowel plus l

In British spelling, verbs ending in a vowel plus l double the l when adding endings that begin with a vowel. In American English, the l is not doubled:

British US
travel travel
travelled traveled
traveller traveler

Words spelled with double vowels

British English words that are spelled with the double vowels ae or oe are just spelled with an e in American English:

British US
leukaemia leukemia
manoeuvre maneuver
oestrogen estrogen

Note that in American English, certain terms, such as archaeology, keep the ae spelling as standard, although the spelling with just the e (i.e. archeology) is usually acceptable as well.

Nouns ending with –ence

Some nouns that end with -ence in British English are spelled -ense in American English:

British US
defence defense
licence license
offence offense

Nouns ending with –ogue

Some nouns that end with -ogue in British English end with either -og or –ogue in American English:

British US
analogue analog or analogue
catalogue catalog or catalogue
dialogue dialog or dialogue

The distinctions here are not hard and fast. The spelling analogue is acceptable but not very common in American English; catalog has become the US norm, but catalogue is not uncommon; dialogue is still preferred over dialog.

Aside from spelling differences, many items and practices have different names in British and American English. To explore further, see British and American terms.