What is the difference between their, there and they're?
Their shows ownership, as in their house. There refers to a place or introduces something, as in over there or there is. They're is a contraction of they are, as in they're happy.
Their is a possessive pronoun, like his or her, used when something belongs to a group: Their dog is friendly. There points to a place, as in Put it there, or starts a sentence, as in There are three apples. They're is short for they are: They're going to the park.
To check which one you need, try replacing the word with they are. If the sentence still makes sense, use they're. If you are talking about something belonging to them, use their. A memory trick: there contains the word here, which is also about place.
Homophones
These three words are homophones, words that sound the same but have different spellings and meanings. They are among the most common spelling mistakes in English, along with your and you're and its and it's. Spell-checkers often miss them because all are real words.
Did You Know?
Another common trio of homophones is to, too and two.