Words such as organize and organise can be written with z or s, with US English using the z form and British English using either z or s. For example:
|organize or organise
|organizing or organising
|organized or organised
|organizer or organiser
|organization or organisation
|recognizable or recognisable
When writing in British English, therefore, you should decide whether to use the z or s spelling, and use the same dictionary or spelling checker throughout for consistency (though see below). In choosing which to use, you should follow any style guidelines of your university, publisher or target journal.
If you wish to make your text more international, using the z spelling reduces the differences between British and US English. In fact, z is the standard British English spelling in the Oxford English dictionaries for example.
Unfortunately, for UK English your word processor may not distinguish between s and z spellings, making consistent computer checking of your document more difficult.
Words pronounced z but written with s in both British and US English
Neither British nor US English uses z or s spellings consistently – both use z and s to varying extents. A list of words that are pronounced z but always written with s, in both British and US English, is given below:#
Words always written with ys in British English