Glove boxes are on the passenger side of a car and are where insurance papers and important operational information for the car are usually stored, along with gloves and knickknacks. These boxes can lock for security purposes but also can be difficult to unlock.

With a Key

Most glove boxes are simple to lock and unlock, requiring the car's key to be inserted into the lock and turned a certain direction to unlock it. This is rather self-explanatory and should be done before the car is started or when the car is pulled over safely to the side of the road and parked. The key should then be removed from the ignition and inserted into the glove box lock. Sometimes these locks can jam and if this happens, jiggling the key is probably your best bet to get it open before you have to go to a mechanic to pry it open for you.

Push Button

On some cars, like luxury car convertibles, the glove box can only be opened with the key inserted and a button pushed on the keyless unlock remote. This is an added security measure to keep people from opening the glove box easily when the convertible is parked and the top is down, allowing access to the interior of the car to anyone passing by. This type of glove box can be unlocked by inserting your key, pressing the unlock button on the remote at the same time and then pulling the level or pushing the button that opens the glove box. If this still doesn't work it may mean there is something wrong with the locking mechanism or motor within the glove box itself.

Source:

Subaru Forester: How to Unlock Glove Compartment

M3 Forum: Unlock Convertible Glove Box