Today's application tend to be more and more decentralised, pervasive, made of autonomous entities or agents, and have to run in dynamic environments. Applications tend to be social in the sense that they enter into communication as human people, and engage into discovery, negotiation, and transactions processes; autonomous programs run their own process, interact with other programs when necessary, but each program lives its life, and a global behaviour emerges from their interactions, similarly to what can be observed in natural life (physical, biological or social systems). Tomorrow's applications are more and more driven by social interactions, autonomy, and emergence, therefore tomorrow's engineering methods have to take into account these new dimensions. Traditional software engineering will not be adapted to this new kind of applications: they do not scale, they do not enable the definition of local behaviours and drawing of conclusions about global behaviours. The scope of this paper is to determine today's and tomorrow's application domains, where such a sociological behaviour can be observed. Starting from the observation of natural life (natural mechanisms used for self-organisation, for anonymous communication, etc), we then discuss how these natural mechanisms can be translated (or have an artificial counterpart) into electronic applications. We also consider software engineering issues, and discuss some preliminary solutions to the engineering of emergent behaviour.