This paper illustrates how, although Service Design has been described as evolving from a narrow description of a phase in New Service Development (NSD) to an approach to Service Innovation, the current Service Design research is still focused on the initial stages of NSD. Comparing existing Service Design research with foundational knowledge on NSD, the authors have proposed two complementary directions for future Service Design studies: 1) the expansion of ‘service design as a phase’ to investigate how Service Design processes and outcomes can be better linked with and integrated within the development and implementation stages of NSD; and 2) the application of ‘Service Design as an approach’ studying how current human-centred design methods could be extended and adapted for service system development and delivery, and how ‘designerly’ ways of innovating could inform the overall NSD process.