Charles Darwin made numerous seminal contributions to the study of animal behavior over his long career. This essay places these contributions in the context of Darwin's life, showing his long-standing interest in psychological and behavioral issues encompassing all species, including humans. Ten areas are highlighted: natural history; communication; sexual selection and courtship; comparative cognition; emotion; instinct and behavioral development; inheritance of behavior; phylogeny of behavior; sociobiology and behavioral ecology; and applied animal behavior, animal welfare, and conservation. Several newer emphases that Darwin anticipated are briefly discussed. Darwin, while not always correct by current standards, crucially aided the process of firmly embedding psychological phenomena in a naturalistic scientific ethos.