In IS outsourcing relationship literature, research has focused on detailed legal contracts and partnerships. We investigate the role of psychological contracts between client and vendor in the IS outsourcing context. The aim of this paper is to put the concept “psychological contract commitment” (PCC) under the spotlight, finding out its mediating effects between legal contracts/partnerships and IS outsourcing success. By analyzing 50 matched survey responses gathered from project managers, vendor firms, and end-users, we found that psychological contract commitment has both direct and mediating effects on outsourcing success. Along the same lines, the key findings suggest that psychological contract commitment explains why legal contracts and partnerships are still crucial to IS outsourcing success.