Continuous change changes everything; it introduces various uncertainties, which may harm the sustainability of software systems. We argue that integrating runtime adaptation and evolution is crucial for the sustainability of software sys- tems. Realising this integration calls for a radical change in the way software is developed and operated. Our posi- tion is that we need to Design for Sustainability. To that end, we present: (i) the AdEpS model (Adaptation and Evo- lution processes for Sustainability) to handle and mitigate uncertainties by means of integrating runtime adaptation and evolution, and (ii) a set of engineering principles to de- sign software systems that facilitate the application of the AdEpS model to build sustainable software.