Many CEOs and managers understand the importance of knowledges sharing among their employees and are eager to introduce the knowledge management paradigm in their organizations. However little is know about the determinants of the individuals knowledge sharing behavior. The purpose of this study is to develop an understanding of the factors affecting the individuals knowledge sharing behavior in the organizational context. The research model includes various constructs based on social exchange theory, self-efficacy, and theory of reasoned action. Research results from the field survey of 467 employees of four large, public organization show that expected associations and contribution are the major determinants of the individuals attitude toward knowledge sharing. Expected rewards, believed by many as the most important motivating factor for knowledge sharig, are not significantly related to the attitude toward knowledge sharing. As expected, positive attitude toward knowledge sharing is found to lead to positive intention to share knowledge and, finally, to actual knowledge sharing behaviors.