This study contributes to insights into mechanisms that influence the successes and failures of emerging energy technologies. It is assumed that for an emerging technology to fruitfully develop, it should be fostered by a Technological Innovation System (TIS), which is the network of actors, institutions and technologies in which it is embedded. For an emerging technology a TIS has yet to be built up. This research focuses on the dynamics of this build-up process by mapping the development of seven key activities: so-called system functions. The main contribution revolves around the notion of cumulative causation, or the phenomenon that the build-up of a TIS accelerates due to system functions reinforcing each other over time. As an empirical basis, an analysis is provided of the historical development of the TIS around automotive natural gas technology in the Netherlands (1970-2007). The results show that this TIS undergoes a gradual build-up in the 1970s, followed by a breakdown in the 1980s and, again, a build-up from 2000 to 2007. It is shown that underlying these trends are different forms of cumulative causation, here called motors of innovation. The study provides strategic insights for practitioners that aspire to support such motors of innovation. (C) 2009 Elsevier Ltd. All rights reserved.