This chapter presents an overview of the human basal forebrain. Most of the systems of the basal forebrain reach the ventral surface of the brain and contribute to its topography. The surface anatomy can be partly delineated with reference to some olfactory structures within or in close relation to the anterior perforated space. The chapter discusses the surface topography of the basal forebrain and reviews its underlying structures. Anteriorally, the surface of the basal forebrain is comprised of the orbitofrontal cortex (OF) laterally, and the gyrus rectus (GR) medially. Immediately caudal to the anterior olfactory nucleus (AO) or retrobulbar area, the orbitofrontal cortex tapers and is replaced by the frontal prepiriform cortex PirF and the ventral claustrum. The ventral limit of the basal forebrain is formed by the nucleus accumbens (Acb) and that part of the ventral striatum that receives olfactory input. Together these comprise the anterior perforated substance.