Growth in the outsourcing market signals that firms of all sizes believe outsourcing will ultimately deliver many benefits and conveniences. But there are not many firms satisfied with the results of outsourcing. What is more, previous researches were fragmentary analyses focused on specific variables of outsourcing such as sourcing decisions, partnership rather than comprehensive analysis. Thus, they could not propose general systematic methodologies applicable to the real situation. To solve these problems, we developed an integrated theoretical framework that considered both contract with the hard side and trust with the soft side from a contingency viewpoint and tested this model using 143 data of Korean companies executing outsourcing. In addition, we examined how situational factors(outsourcing task complexity and outsourcing management competence) affects each path in the research model. The results of this study are as follows. First, it was proved the theory that trust is not a substitute for contract but its complement. Previous empirical studies on outsourcing success factors were focused on the establishment of successful partnership on the assumption that trust can replace contract in many situations. According to the results of our empirical analysis, however, contract and trust were in a mutually complementary relation with each other and their emphasis was different. Furthermore, different from previous researches, it was found effective to use trust as a supplementary tool and contract as a main means in outsourcing management strategy. Second, this study provided an integrated view that sees both contract and trust from a contingency viewpoint in theoretically reestablishing the relationship between contract and trust. Previous researches leaned to specific variables or theory-centered fragmentary analysis, but this study proposed a more practical and integrated research model and tested its effectiveness. Based on the results, with the model, decision makers are expected to scrutinize outsourcing situation more closely and to have a practical insight to the situation. Third, it was found that contract mechanism and trust building do not have a direct effect on outsourcing performance but relationship management intensity mediates the effect of contract mechanism and trust building. This is considered significantly meaningful to outsourcing partners who have believed that outsourcing would be successful if a contract is made properly or trust is built. Lastly, the path from trust building to relationship management intensity was moderated by informed buying, as the path coefficients from trust building to relationship management intensity varied by the degree of informed buying competence.