Species-specific evolutionary pressures have directed sensory system modifications resulting in a diversity of sensory capabilities and adaptations across species. For numerous species, these variations have been directly influenced and harnessed by humans throughout history. The modern domestic dog is a prime example, and its superior sense of smell and sociability has enabled its use as a biological sensor to aid in human-directed activities of benefit to individuals and society. Performance in these activities can be impacted by physical, psychological and environmental factors. Exploring the capabilities and limitations of these working animals involves understanding their anatomy, physiology and cognitive processes.