The paper investigates the impact of distance, contiguity and technological proximity on cross- regional knowledge flows, by comparing the evidence concerning co-inventorship, applicant-inventor relationships and citation flows. We find evidence of significant differences across these diverse kinds of knowledge flows for what concerns the role of distance, and the moderating role of contiguity and technological proximity. Moreover, we show that border effects may prove crucial in a twofold sense. On the one hand we show that contiguity between regions belonging to two different countries still plays a moderating role, although weaker as compared to that of within-country contiguity. On the other hand, regions sharing a frontier with a foreign country are more likely to exchange knowledge with this foreign country than other regions which are far away from the border.