This chapter introduces the importance of trust in knowledge management system building. It argues that the relationships among organizational culture, problems of knowledge sharing, and HR features are in close correlation with each other. The main aspect of the chapter is to show the general requirements and pre-requisites of knowledge management system building based on trust. The authors aim to reveal the theoretical aspect of trust-based culture and knowledge management system building, and the HR's tasks connected to these two ideas. The chapter presents three case studies on three different companies' practices, a multinational, big company, and an institution. This chapter shows samples, best practices, critical steps that can ensure success to the companies that want to start building a knowledge management system.