The largest paranasal sinuses are the maxillary sinuses, a pair of pyramid-shaped air spaces inside the maxilla (upper jaw bone), one on each side of the nasal cavity below the eye sockets.
Each maxillary sinus drains into the middle meatus of the nose through the semilunar hiatus. The other paranasal sinuses are the frontal, ethmoid, and sphenoid sinuses, all of which are smaller.
Source: Maxillary sinus, Wikipedia