In an era of climate change, the process of and time frame for fostering new industries with the capacity of being innovative and able to diffuse a wide range of renewable energy technologies on a large scale has become a pressing issue. In the midst of the creation of such industries are the system builders―without such actors, new technologies and industries would not emerge. In this thesis, a novel conceptualisation of system builders is presented from a technological innovation system (TIS)perspective. The focus is on system builders with the intention of realising the potential of biomass gasification for the production of second-generation transportation fuels and other chemicals. The empirical work covers the historical development of biomass gasification in four countries―Austria, Germany, Sweden, and Finland―leading up to the nine most prominent technology development projects currently in Europe. This thesis analyses: a) who act as system builders in the different national contexts; b) how they learn and enable the emergence of the new system; and c) the limits to their capacity in creating the new and embryonic industry structures. With these insights, policymakers may d) set more realistic goals with respect to future targets and design policy interventions that address the actual system weaknesses of the emerging TIS. It is suggested that second-generation fuels from biomass can only play a very limited role in the fuel market until 2020 at the earliest. For realising the large but long-term potential of the technology, actions must now be taken to shift some of the risks for investors to society at large by funding demonstrations and forming initial markets for fuels that are significantly more expensive than conventional alternatives. Without such markets, the system builders will have great difficulties attracting further actors with complementary competencies, as well as the additional resources necessary to resolve the remaining technical uncertainties and take the required steps towards commercial-scale plants