There are many spelling differences between American and British English. In some cases, the same word will be spelled one way in American English and another way in British English. There are times when this inconsistency is very confusing. Realize and realise fall under the same category and if you need to know the difference between the two spellings, keep reading.
Realize as verb:
His worst fears have been realized.
Use of realise:
Realise is the British spelling of this verb. It means to become aware of something or to bring something into being. When writing for British audience, make sure you use these spellings and stick to them in your writing.
Use of realize:
Realize is the American spelling of this verb. It can be used in any of the same contexts as realise. When writing for American audience, make sure you use these spellings and stick to them in your writing.
Realise or realize:
Realise and realize are two variants of the same word. One spelling is more common in American English, while the other is more common in British English. Since both of these forms are accepted somewhere in the world, neither is technically wrong. Still, any time you are writing, you should consider your intended audience. This principle extends to spelling differences, as well. You will want to use British spellings when writing for a primarily British audience, and American spellings if you are writing for a predominantly American audience. You can remember to reserve realize for American audiences since it contains a z, like Arizona. Arizona is in America, so it will be easy to remember that realize is preferred in American English.