The Master's thesis studied the influence of organisational culture on knowledge sharing, and the promotion of knowledge sharing in an expert organisation. The goal of the commissioned study was to develop knowledge sharing practices at Fingrid Oyj and to define characteristics of a target culture to which the company management can commit and towards which the organisational development can be steered. The study was mainly implemented in the form of qualitative research, and the research method was action research. Earlier studies dealing with the connection between knowledge sharing and organisational culture were reviewed in the thesis. The case company employees' views of the current state of their organisational culture were surveyed using the competing values framework by Cameron & Quinn. The organisation's documentation, strategy, values, and guidelines were reviewed as a desk study. In addition, 10 themed interviews concerning the company's organisational culture and methods of promoting knowledge sharing were conducted. The research results indicate that the organisational culture and knowledge sharing are connected. Apart from previous research results, this was also supported by the case company's practices. Cultures featuring open interaction, shallow hierarchies of authority relations, and encouragement of collective work instead of individual performance also favour knowledge sharing instead of holding back information. Hierarchic and group-centric characteristics proved to be dominant in the case company's organisational culture. The hierarchic nature is reflected in the abundance of rules and guidelines in the company's operational manage-ment but, nevertheless, the company has an informal atmosphere, a shallow organisational model and a decision-making system that delegates decision-making power downwards in the hierarchy. It was stated that the company culture supports knowledge sharing practices. The action research resulted in a definition of target culture characteristics for Fingrid Oyj, which was carried out in co-operation with the top company management, a framework for how the culture should be reflected in supervisory work, and suggestions on the further development of knowledge sharing practices in the company.