Essential oils (EOs) have served a key role in the evolution of the animal and plant kingdoms. Many of the chemical components that make EOs so powerful have been identified, facilitating a deeper understanding of how nature’s vast array of fragrances may provide medical benefits. EOs affect animals on a physical and emotional level, through the interaction with the neuroendocrine, circulatory, and other body systems. In the clinical veterinary setting, EOs may be incorporated as primary or adjunctive therapy. With adherence to safe use guidelines, EOs may be used in companion animals with a low risk of adverse events.