This chapter discusses anatomy and physiology of PNS, which is a group of air containing spaces that surround the nasal cavity. Maxillary sinus is also called antrum of highmore and is the largest sinus in the body of maxilla. Pterygopalatine fossa is a triangular space between maxilla, palatine and pterygoid process of sphenoid, and it contains internal maxillary artery, vidian nerve and sphenopalatine ganglion. Veins drain into anterior facial vein and pterygoid venous plexus. Lymphatics drain into submandibular lymph nodes. Nerve supply is by maxillary nerve through superior alveolar, anterior palatine and infraorbital nerve. Secretomotor fibres relay through pterygopalatine ganglion. Frontal sinuses are two in number and are of unequal size divided by a bony septum which is seldom in the midline. Sphenoid sinuses are contained in the body of sphenoid bone and are situated in the posterior part of nasal cavity. Blood supply is by the posterior ethmoid and sphenopalatine artery.