This thesis explores the development of the urban structure in the Greater Oslo Region between 2001 and 2015, with the aim of discovering if the region has developed towards a polycentric structure. The development of population size is used as an indicator of morphological polycentricity, while the development of commuting patterns is used as an indicator of functional polycentricity. 6 regional cities, Sandvika, Asker, Lillestrøm, Jessheim, Ski and Ås, are analysed and compared to Oslo, the dominant centre of the region. The thesis finds that population has increased at a roughly similar annual growth rate in total for the regional cities as Oslo, and there is thus no indication of increased morphological polycentricity from 2001 to 2015. However, the share of the Greater Oslo Region population that commutes to the regional cities has in total increased slightly, and the share of the population that commutes to Oslo has decreased. At the same time the regional cities have slightly increased their reach as commuting destination, while Oslo's reach has decreased. The results indicate that the urban structure has become slightly more functionally polycentric from 2001 to 2015.