This paper explores the strategic goals behind actors’ involvement in emerging technological innovation systems (TISs) for sustainable technologies and the way they contribute to the development of the TIS functions. Based on six expert interviews with firms within the biorefinery sector in Germany, we observe four different strategic goals driving firm-actors’ involvement: (1) exploiting new markets and businesses, (2) learning about the potential of new markets and businesses, (3) developing new technologies and (4) building up new market applications. We also differentiate between three firm-actor types: (1) a leading type of incumbent firm highly contributing to the TIS functions; (2) a learning type of incumbent firm with lower contribution; and (3) a ‘fill the gap’ type of SME or start-up producing complementary knowledge or connecting other TIS actors.