Lorenz was the father of modern ethology, the analysis of animal behaviour. This, his supposed last work, until the discovery of the so-called `Russian manuscript' (The Natural Scince of the Human Species) is a synthesis of his lifetime work on one particular animal, the Greylag Goose. It provides a guide to the development of his theories of behaviour and the thinking behind his research, as well as giving a complete description of the private life of the Greylag.