The study of animal behaviour has become one of the fastest growing b- logical disciplines in recent decades. This development can be easily - ferred, for example, from the steady increase in the total number of pub- cations on any aspect of animal behaviour, in particular also in journals with a more general readership (e. g. Nature, Proceedings of the Royal - ciety or Current Biology), the ever-increasing number of participants at - ternational conferences (e. g. IEC or ISBE), and from the growing numbers of students choosing courses in this field. This development has several causes, of which I find three particularly compelling. First, it is incre- ingly being appreciated that behaviour is the crucial level at which an in- vidual's genotype and phenotype interface with the environment. Rec- nising behaviour as the main mechanism animals employ to ascertain their homeostasis, growth, survival and reproduction therefore provides a deep understanding of organismal integration and adaptation. Second, the ast- ishing success of the study of animal behaviour also has importantly to do with the intellectual flexibility and methodological inter-disciplinarity - quired for comprehensive analyses of behaviour. Today, students of beh- iour are jacks-of-all-trades; importing, applying and improving methods from many neighbouring disciplines, such as molecular genetics, physi- ogy or micro-electronics, as well as concepts and theories from less ob- ous sources, such as economics or sociology, for example.