Apart from the 20-year anniversary in 2014 of the first publication of the GERAM ('Generalised Enterprise Reference Architecture and Methodology') Enterprise Architecture Framework, the timeliness of this paper lies in the new interest in the use of systems theory in enterprise architecture (EA), and consequently, 'light-weight' architecture frameworks (AFs). Thus, this paper is about the use of systems thinking and systems theory in EA and about how it is possible to reconcile and understand, based on a single overarching framework, the interplay of two major enterprise change endeavours: on one hand enterprise engineering (i.e. deliberate change) and on the other hand evolutionary, organic change. The paper also demonstrates how such change processes can be illustrated by employing systems thinking to construct dynamic business models; the evolution of these concepts is exemplified using past applications in networked enterprise building, and more recent proposals in environmental-, disaster- and healthcare management. Finally, the paper attempts to plot the way GERAM, as a framework to think about the creation and evolution of complex socio-technical systems, will continue to contribute to the society in the context of future challenges and emerging opportunities.