The recent resurgence of growth studies has indicated technological activities and knowledge spillovers as one of the most important factors in determining the performance of the economic systems. However, only few empirical studies have tried to analyse the flows of technology across regional economies due to the lack of adequate indicators. In this paper we propose new evidence on the characteristics of knowledge spillovers across the European regions based on a database on patents citations developed at the NBER . The data refers to patents granted by the US patent office to European firms over the period 1978-1997. First, we have assigned each patent to 147 European regions according to the place of residence of the first inventor. Then, we have examined in- and out- flows of patent citations as proxy of knowledge spillovers. In order to asses both the spatial and network characteristics of these flows we have tried to combine methodological instruments developed within the Social Network Analysis and the Geographical Information Systems. Our analysis shows the huge differences that exist among high tech and traditional sectors in the complexity of technological networks and in the geographical distribution of knowledge flows.