The olfactory system is the sensory system used for olfaction or the sense of smell.

Most mammals and reptiles have two parts to their olfactory system.

1. There is a main olfactory system, which detects volatile, airborne substances.
2. There is secondary, or accessory, system. The accessory olfactory system senses fluid-based stimuli. Behavioral evidence indicates that most often, the stimuli detected by the accessory olfactory system are pheromones.

The olfactory system is often spoken as being similar to the gustatory system (taste system). Both are chemosensory senses. They change chemical signals into nerve impulses, which are translated into perceptions in the brain.

Position of mygdala in each hemisphere of the human brain