Studies have emphasised the importance of a strong relationship between a client and vendor to ensure positive IT Outsourcing (ITO) outcomes. To measure and assess this relationship strength, a construct known as Relationship Quality (ReQ) has been widely used in the ITO context. However, recent studies have highlighted the inconsistent and even contradictory application of this construct in previous studies raising concern over its validity. To address this matter, we conducted a critical literature analysis to systematically examine how ReQ has been applied in previous ITO studies. The findings from our review highlight three important knowledge gaps with the current ITO studies: 1) lack of rich qualitative studies investigating ReQ that is complex and subjective in nature; 2) inappropriate application of economic and strategic based theoretical lenses; 3) lack of differentiation between ReQ attributes. This study provides a number of recommendations to enhance the application and measurement of ReQ in future ITO studies. The next step of the study will address the three identified knowledge gaps. This study offers important implications to both theory and practice.