What is the difference between 'its' and "it's" and how do I never confuse them?

'It's' with an apostrophe is a contraction of 'it is' or 'it has'. 'Its' without an apostrophe is the possessive form, meaning belonging to it. The trick is simple: whenever you write 'it's', expand it to 'it is' or 'it has' and check if the sentence still makes sense. If it does, keep the apostrophe; if it does not, use 'its'. For example, 'It's raining' expands to 'It is raining', which is correct. But 'The dog wagged its tail' cannot become 'it is tail', so it must be the possessive 'its'. Remember that possessive pronouns like its, his, hers and theirs never take an apostrophe, even though we add apostrophes for possession with nouns.