This paper aims at contributing to the research on knowledge spillovers and their spatial extent by presenting new empirical evidence on a key mechanism driving and directing knowledge diffusion processes, namely, the mobility of knowledge and highly-skilled workers. The analysis is based on a rich data set on US inventors and their patents filed at the European Patent Office from 1978 to 2004. Findings indicate that two distinctive spatial patterns can be detected: inventors move both at short and large spatial distances (i.e., three hours and more than 8 hours driving distance, respectively) in similar proportions. Interestingly, in the largest innovative urban areas inventors' inflows and outflows primarily involve distant rather than neighbour areas.