The aim of this paper is to make the case for a systematic engagement of transition studies with complexity theory and research. We argue that transition research is important for the understanding and development of possible sustainable future pathways. However, there are several controversies in transition research, including, the role of agency in transitions; the relationships between levels (niche, regime and landscapes); the origin of transitions; the identification of a transition, including starting and ending point of transition processes; and the paradox of replicability and scaling up of independent experiments. We argue that transition research, and future studies can benefit from taking complexity theory seriously. In the paper, we elaborate four insights from complexity studies that can move the research agenda of transition studies forward: empirically investigating the degree of complexity of a system; investigating complexity at the level of the policy-making system; longitudinal and retrospective research designs for the identification of transitions; methodological tools which accommodate complexity, such as agent-based modeling and ARIMA modeling. Further, we suggest how these can improve our knowledge of transitions towards sustainable future.