This paper reviews the literature on technological innovation systems (TIS) to explore how TIS studies have contributed to building the understanding of innovation processes driving sustainability transitions. We summarise the conceptual and methodological advancements in the TIS studies at three levels: (1) meso-level focused on TIS functions and structures; (2) macro-level explaining the TIS-context interactions; (3) micro-level elucidating the role of actors, agency and social interactions in a TIS. We argue that to improve the understanding of how innovation processes contribute to sustainability transitions, future TIS studies, at various levels, should further elaborate (1) the dynamics in mature and declining TISs, (2) the relation between TIS processes and structural change and (3) the directionality of socio-technical change. Such advancements in the field would enable more transformation-oriented policy recommendations from TIS studies.
