Use -ise endings, not -ize.
Follow British English for spelling.
Note: There are a small set of verbs in English which must always be spelled with -ise at the end and never with -ize. Here are the most common ones:
|chastise||disguise||prise (meaning "open")||surprise|
Exception: CERN is the European Organization for Nuclear Research. Note the "z". Use "the Organization" for CERN, otherwise "organisation".
There is one more exception to the rule that we use at CERN: spell "analyse" with an s.