The rapidly increasing pervasiveness and integration of computers in human and animal society calls for a broad discipline under which this development can be studied. We argue that to design and use technology one needs to develop and use models of humans/animals and machines in all their aspects, including cognitive and memory models, but also social influence and (artificial) emotions. We call this discipline Behavioural Computer Science, and propose that behaviour computer science models try to unify (models of) the behaviour of humans/animals and machines when designing any ICT systems. Incorporating empirical evidence for actual human behaviour instead of relying on assumptions about rational behaviour, is one of the contributions of this paper. We must also acknowledge that advancements in AI will give machines capabilities that from many perspectives are indistinguishable from those of humans/animals. We provide a few directions for approaching this challenge, focusing on modelling of human and machine behaviour as well as their interaction.