Inter-organisational knowledge transfer is of central interest both as an academic topic and in business practice. However, despite the attention given to the importance of this subject from different perspectives in various contexts, little is known about how knowledge is transferred from vendors to clients in information systems (IS) outsourcing. This research attempts to address this apparent theoretical and empirical deficiency by providing a deeper understanding and more holistic analysis of the key factors which facilitate or inhibit knowledge transfer success in IS outsourcing. This study employed a qualitative, multiple case study approach in the interpretive paradigm. Data was collected mainly from the IS departments of three public sector organisations in Oman. Oman was chosen as the context for the study due to its rapid growth in recent years and the opportunity to consider the many major IS outsourcing projects which have been undertaken by its public sector. Through semi-structured interviews, this study explored the perspectives of the internal IS staff on their experience of knowledge transfer and learning from vendors through various IS outsourcing projects. Written and electronic documentations as well as non-participant observations also served as important triangulation and complementary sources in understanding the phenomenon being studied and as means of gaining additional perspectives and further insights on key issues. The empirical evidence demonstrated that there are five sets of factors which facilitate or inhibit knowledge transfer success in IS outsourcing. These are: knowledge (knowledge tacitness and knowledge complexity), client (learning intent, absorptive capacity and motivation), vendor (vendor capability, vendor credibility and vendor openness), relationship (relationship quality, relationship duration, relationship governance and organisational distance) and knowledge transfer mechanisms (formal and informal). The findings of this study contributed and extended the growing body of research on IS outsourcing by developing a novel, holistic conceptual framework which examined five sets of factors that impact knowledge transfer success. Additionally, it provided prescriptive value for practitioners seeking to realise efficient and effective knowledge transfer in IS outsourcing.