Ethology (from Greek: ἦθος, ethos, "character"; and -λογία, -logia, "the study of") is the scientific and objective study of animal behaviour, and is a sub-topic of zoology. The focus of ethology is on animal behaviour under natural conditions, as opposed to behaviourism, which focuses on behavioural response studies in a laboratory setting.

Many naturalists have studied aspects of animal behaviour throughout history. The modern discipline of ethology is generally considered to have begun during the 1930s with the work of Dutch biologist Nikolaas Tinbergen and by Austrian biologists Konrad Lorenz and Karl von Frisch, joint winners of the 1973 Nobel Prize in Physiology or Medicine. Ethology is a combination of laboratory and field science, with a strong relation to certain other disciplines such as neuroanatomy, ecology, and evolution. Ethologists are typically interested in a behavioural process rather than in a particular animal group, and often study one type of behaviour, such as aggression, in a number of unrelated animals.

The desire to understand animals has made ethology a rapidly growing field. Since the turn of the 21st century, many aspects of animal communication, animal emotions, animal culture, learning, and even sexual conduct that experts long thought they understood, have been re-examined, and new conclusions reached. New fields have developed, such as neuroethology.