This chapter provides an overview of the anatomy of the primary olfactory system, the olfactory mucosa and olfactory bulb. A notable feature of olfactory bulb anatomy is the convergence of feedback from higher centres whose axons project onto the interneurons at the granule and periglomerular levels. The chapter shows how the chemical properties of odorant molecules are encoded into neural activity. It covers the consequences of this neural activity and how it defines the regions of the human brain involved in olfactory perception. The olfactory system is characterised by relatively direct connections to brain structures implicated in memory and emotion such as the hippocampus, thalamus, and frontal cortex. With the development of functional magnetic resonance imaging (fMRI) and positron emission tomography (PET), it is possible to reveal large-scale activation patterns associated with particular cognitive processes, allowing the identification of the neural networks specifically activated by chemosensory stimuli.