Hermione was given the Time-Turner by Professor McGonagall under the instructions of Professor Albus Dumbledore. She was given the Time-Turner because she wanted to study several subjects together in her third year, but would not be able to because some of those classes were held at the same time. Instead of having to face the impossibility of having to sit in two classes simultaneously, she was given this device so that she could go back in time after every class to attend the other classes she missed.