Sinus and skull base surgeons have witnessed a recent shift from open approaches to less invasive endoscopic surgical treatment of sinonasal and skull base pathologies. However, operating in a narrow surgical space surrounded by vital structures with endoscopes can be challenging and requires exquisite surgical technique, excellent knowledge of anatomy, and cognizance of possible anatomical variations. In this chapter, we discuss the important anatomical features of the nasal cavity, orbit, and anterior skull base, variations in anatomy, and the importance of surgical landmarks to remain safe during endoscopic surgery.