Over the past decade, research on animal personality has flourished in numerous disciplines ranging from Behavioral Ecology and Developmental Psychobiology to Genetics and Comparative Psychology. The broad appeal of animal studies is that, in comparison with human studies, they afford greater experimental control, more options for measuring physiological and genetic parameters, greater opportunities for naturalistic observation, and an accelerated life course. Past research has established that personality (a) exists and can be measured in animals; (b) can be identified in a broad array of species, ranging from squid, crickets, and lizards, to trout, geese, and orangutans; and (c) shows considerable cross-species generality for some dimensions. The wave of new studies is shedding fresh light on traditional issues in personality research (How do early experiences affect adult personality?), raising novel questions (What are the evolutionary origins of personality traits?) and addressing practical problems (Which dogs are best suited to detecting explosives?).