Agile software development methods are often advertised as a contrast to the traditional, plan-driven approach to software development. The reported and argued benefits on software quality, coordination, productivity and other areas are numerous. The base of empirical evidence to the claimed effects is however thin, and more empirical studies on the effects of agile software development methods in different contexts are needed, especially in large-scale, industrial settings. The purpose of the thesis was to study the impact of using agile principles and practices in large-scale software development projects at Ericsson and it was carried out as a multiple-case study of two projects. One of the projects had implemented a limited number of agile software development practices and was largely plan-driven, while the other project had fully adapted its organization and product design for agile software development. Propositions of possible effects of the use of agile principles and practices in the two projects were generated by a literature review. Empirical data was then collected from online surveys of project members, internal documents, personal contact with key project members and a collection of metrics, to study the presence of the proposed effects. The study was focused on eight different areas: internal software documentation, knowledge sharing, project visibility, pressure and stress, productivity, software quality and project success rate. Agile principles and practices were found to: Lead to a more balanced use of internal software documentation, when supported by sound documentation policies. Contribute to knowledge sharing. Increase project members’ visibility of the status of other teams and the entire project. Increase coordination effectiveness and reducing the need for other types of coordination mechanisms. Increase productivity. Possibly increase software quality. Additionally, the study showed that internal software documentation is important also in agile software development projects, and cannot fully be replaced with face-to-face communication. Further, it was clear that it’s possible to make a partial implementation of agile principles and practices, and still receive a positive impact. Finally, the study showed that it’s feasible to implement agile principles and practices in large-scale software development. It therefore contributes to understanding the effects of agile software development in different contexts.