HIS book is not intended as an exhaustive review T of facts. Its aim is rather the presentation of a bio- logical approach to the phenomena of social behaviour. This type of approach was revived by Lorenz's pioneer studies. It is characterized by emphasis on the need for renewed and careful observation of the huge variety of social phenomena occurring in nature; by emphasis on a balanced study of the three main biological problems- function, causation, evolution; by emphasis on an appro- priate sequence of description, qualitative analysis, quanti- tative analysis; and finally by emphasis on the need for continuous re-synthesis. The character of this approach, combined with the limitations of space, have determined this book's contents. Limits of space led to the omission of a great deal of de scrip- tion. Thus, Deegener's voluminous work on fhe multitude of types of animal aggregations has not been discussed. Also, the highly specialized 'states' of social insects have not been treated in detail, since there are excellent books dealing exclusively with them.