After more than 25 years of research on information technology outsourcing (ITO) in general and ITO client-vendor relationships in particular, an already comprehensive body of knowledge is available on this important topic and related phenomena. This study sheds further light on the existing knowledge on ITO client-vendor relationships by applying social network analysis and content analysis methodologies. Based on our approach, we were able to (1) evaluate key articles, authors, and journals covering the research topic, (2) analyse the development of ITO client-vendor related research in the last 10 years and, most importantly, (3) identify gaps in our knowledge on ITO client-vendor relationships. Specifically, our research identified several gaps in our knowledge on important ITO client-vendor relationship concepts such as trust, control, and knowledge transfer. In accordance to Lacity et al. (2010), our results show the need for indigenous theories on ITO as a next step in further enhancing our understanding of the topic. We emphasize further research on ITO client-vendor relationships and provide distinctive research directions for the research community.