American and British English
You now know that British and American English often spell the same word differently. In British English verbs that can be spelt with either –ize or –ise at the end are always spelt with –ize at the end in American English. Examples are:
British                               American
apologise/apologize           apologize
memorise/memorize           memorize
organise/organize              organize
realise/realize                     realize
recognise/recognize           recognize


Of course, you can choose whether you’d rather use the American or British way of writing. Just be consistent.