This chapter provides background focusing on the anatomy and physiology of the olfaction in an effort to help canine handlers and others involved in the use of canines in forensic investigations. The nares, nasal turbinates, olfactory sensory cells, olfactory receptors, and corresponding part of the central nervous system are covered. The role that each of those parts play in olfaction is included, describing how a dog is able to accomplish what they can when it comes to smelling and perceiving the world around them. Differences between species (human and canine) and differences between breeds or types of dogs are discussed.