The partnership between humans and domestic animals is natural. The human brain is hard-wired to emotionally respond to animals. Beginning with the domestication of wolves, this chapter covers the process of domestication and reviews the early work of behaviorists and ethologists who refused to accept emotional states in animals. Modern behavior research employs methods developed by behaviorists and ethologists combined with neuroscience and genetics. Emotional systems in the brain drive behavior. Confusion between different emotional systems may explain conflicting findings in the behavior literature. Behavior in an open-field test may be motivated either by fear, separation distress, or novelty seeking. Each emotion is controlled by separate subcorticol systems. A novel open-field arena can frighten a prey species, but it may activate seeking in a predator. Genetics affects the strength of fear, novelty seeking, and separation distress. Behavior is shaped by a complex interaction between genetics and experience.