Research and development service firms (RDSFs) are a particular type of technology-based knowledge-intensive business services (KIBS). RDSFs provide clients with R&D services on a contract basis, and operate as knowledge intermediaries linking research and market. They are innovative in their own right, as well as supporting innovation efforts by their clients; they rely on their own innovation efforts to be competitive and to develop new value propositions for their clients. The present paper explores the innovation process in RDSFs, drawing on semi-structured interviews with founders and senior managers of 32 companies in the United Kingdom. Our findings suggest that RDSFs vary considerably in terms of their primary innovation drivers (i.e. whether they are mainly driven by market demands or by technological opportunities) and the outcomes they pursue (i.e. whether their outputs are mainly services to clients or a mixture of services and products and/or intellectual property). Four major orientations of RDSFs were identified: (i) technology-based innovation exploiters; (ii) science-focused innovation explorers; (iii) client-driven innovation integrators; and (iv) open innovation translators. This variety among firms normally belonging to the same, small subsector of KIBS, suggests the need for caution in generalising about behaviour in terms of such statistical groupings.