The maxillary sinus is generally the largest paranasal sinus and can be affected by sinogenic or odontogenic inflammatory and infectious disease, as well as by benign or malignant neoplasias. The maxillary sinus is often the first sinus to be opened during endoscopic sinus surgery, and its boundaries serve as important landmarks during endoscopic sinus and skull base surgery. This chapter outlines surgically pertinent anatomy and technical steps of different surgical approaches to the maxillary sinus.