Ecosystem services research has become a major academic field, drawing in various academic disciplines, perspectives, and research approaches. The multifaceted concept of "ecosystem services" includes a normative component, which has strong implicit links to the notion of sustainability. Yet, how ecosystem services research relates to sustainability has received little attention. We reviewed the current state of research on ecosystem services, and examined whether the concept's original motivation has allowed it to act as an effective boundary object for the integration of the diverse knowledge related to sustainability. A full-text, multivariate statistical analysis of 1388 peer-reviewed publications on ecosystem services from 1997 to 2011 revealed a rapidly growing but fragmented body of research, which has emphasized the development of descriptive understandings of human-nature interactions. Future challenges for the ecosystem services concept include greater integration of currently fragmented knowledge domains and stronger engagement with the concept's normative foundations.