Part 1 Feeding ecology: food availability; brown hyaena diet; spotted hyaena diet; diets of the other large carnivores and ecological separation of the predators; the impact of predation on the prey populations; relations between hyaenas and other carnivorous animals. Part 2 Comparative foraging and feeding behaviour: activity patterns and resting sites; foraging group sizes; the use of senses during foraging; foraging for vegetable matter, birds' eggs and insects; brown hyaena hunting behaviour; spooted hyaena hunting behaviour; feeding behaviour. Part 3 Social structure and spatial organization: brown hyaena clans; spotted hyaena clans; nomadic males; land tenure system; factors affecting the sizes of social groups and territories. Part 4 Communication patterns and social interactions: visual and tactile communications and social interactions; vocalizations; scent marking. Part 5 The comparative denning behaviour and development of cubs: dens; development of cubs; sub-adults; functional considerations of denning behaviour in the Hyaenidae. Part 6 The individual in hyaena society: degrees of relatedness between clan members; brown hyaena society; spotted hyaena society; evolutionary trands in the social systems of the two species. Part 7 Relations between, and management considerations for, brown hyaenas and spotted hyaenas. Appendices: 1 - common and scientific names of species mentioned in the text; 2 - estimated numbers of some ungulates in the spotted hyaena study area; 3 - ageing criteria of ungulates based on eruption of teeth in bottom jaws and tooth wear; 4 - methods used to measure territory sizes; 5 - degrees of relatedness between clan members.