Minimally invasive endoscopes with excellent deep observation capabilities are effective means for surgery for intraventricular lesions. The ventricles have a complex three-dimensionally structure, and important structures around the ventricles may causes symptoms even with slight damage. Therefore, familiarity with the ventricular anatomy and protective manipulations are important. During endoscopic observations in actual surgery, the ventricular wall is entirely covered with the ependymal tissue, limiting the visibility of landmarks. Furthermore, when distorted by the tumor, the anatomical orientation may be lost, and identifying the lesion can be difficult. In this chapter, we describe the ventricular anatomy under endoscopic observation using actual photographs and illustrations based on anatomical landmarks, in order to safely perform intraventricular surgery.