Personas are fictitious characters that represent the needs of the intended users, and scenarios complementing the personas describe how their needs can be met. The present doctoral thesis considers the usage of personas and scenarios and how they are used in system development projects. The study is motivated by the relative lack of empirical data on the persona method in actual use. The study was carried out in the context of a large international research project called Nepomuk and involved two conceptually dif­ferent field studies. On the one hand, field studies in user settings were conducted, which aimed at creating personas and scenarios, and for which a user-centered design approach was applied using partici­pant observation, contextual interviews, video brainstorming and proto­typing. On the other hand, a field study in the setting of the Nepomuk project itself was conducted, which aimed at observing how the per­sonas and scenarios were received and used in the project work. The work conducted in the project setting was a multi-sited ethnographic field study, which was documented through ethnographic writing. The project setting field study showed that the persona method was difficult to put into consistent use, and the support of persona advocates guiding usage would have been helpful. The method was used without much effort to communicate about the needs and desires of the intended users, but was less successful in compelling project members to use personas and scenarios during various design activities. The field study also revealed alternative usages of the method that can be supported and utilized. The contributions of the thesis include an account of the effect the storytelling aspect has on the creation as well as usage of personas and scenarios. Also, the essential elements of constructing personas and scenarios are discussed as well as the prerequisites for making personas and scenarios support the design process in system development projects. Lastly, the thesis describes how personas and scenarios can support the communication of user needs and desires to project members and stakeholders as well as support design activities in system development projects. / QC20100629