Zero emission buses (ZEBs) have become an important part of the transition to sustainable urban transport. In 2016 the Dutch Ministry of Infrastructure and Environment and 14 transport authorities signed a “Zero Emission Regional Public Transport by Bus” administrative agreement, stating that from 2025 onward all new buses must use 100% renewable energy and from 2030 all buses must be fully emission free. Since then the Dutch public transport system has added more than 1000 battery electric and hydrogen fuel cell buses to their bus fleet. These shifts towards increased sustainable mobility are influenced by policy changes and innovation in technology and institutions. In order to explain how such complex socio-technical transitions develop, it is therefore important to look at them from both a socio-technical and a policy perspective. Technological innovation and policy innovation are analyzed in different research fields, namely innovation studies and policy studies. In policy theory technological changes are considered as exogenous events, which can also be said about the multiple streams framework (MSF). It does not consider the differences in innovation patterns of technologies, which is the case in most policy literature. Meanwhile in technology transition theory policy changes are seen as a mere black box, which can be seen in the multilevel perspective (MLP) as well. It does not include the ways that policies develop. This makes it difficult to identify important policy-technology feedback links and dynamics in sustainability transitions. This research looks at the way in which the MLP and the MSF complement each other in order to provide a more holistic explanation of sustainability transitions and how this can be used in future research for theory synthesis. This will be done through a case study of the ongoing transition to ZEBs in the Dutch public transport sector. The aim of this research is to find ways in which the two frameworks strengthen one another, based on the findings of the case study. The results will then be used to generate a proposition to help synthesize and develop a conceptual framework in future research, which combines the MSF and MLP in order to have a more comprehensive explanation of sustainability transitions.