The perception of the value and propriety of modern engineered systems is
changing. In addition to their functional and extra-functional properties,
nowadays' systems are also evaluated by their sustainability properties. The
next generation of systems will be characterized by an overall elevated
sustainability -- including their post-life, driven by efficient value
retention mechanisms. Current systems engineering practices fall short of
supporting these ambitions and need to be revised appropriately. In this paper,
we introduce the concept of circular systems engineering, a novel paradigm for
systems sustainability, and define two principles to successfully implement it:
end-to-end sustainability and bipartite sustainability. We outline typical
organizational evolution patterns that lead to the implementation and adoption
of circularity principles, and outline key challenges and research
opportunities.