This paper presents reflections on how sustainable development (SD) is defined as a research topic and on differences in references to SD in research. The paper argues that the reference of SD as a research topic must expand to include a broader range of research subjects. During two years of methodical discussions and workshops conducted through the interdisciplinary postdoctoral research group Sustainable Future at the Universität Hamburg (Germany), the authors have observed that SD has played a major role in natural sciences (i.e. environmental and earth system sciences) and engineering, and a far lesser role in the social sciences and humanities (SSH). This imbalance in the discourse on SD in research impedes a full understanding of the diverse tasks and challenges that must be addressed in SD. An integrated approach is suggested to unite perspectives from natural sciences, engineering and SSH. The authors therefore encourage a more explicit notion of the concept of SD in SSH research, which builds upon and goes beyond current approaches to SD in SSH. The paper presents some illustrative examples which investigate the implications of expanding or restricting the disciplinary boundaries of sustainability research. The examples advocate an inclusive approach for which the authors describe and clarify several methods for expanding research towards cross-disciplinary methods. To this end, the authors present some practical recommendations for the integration of sustainability into the design and implementation of research academic practice. The paper closes up with an argument that all disciplines should expand their definition of sustainability in order to hasten research outcomes from all the diverse sectors of sustainability research.