This chapter reviews relevant contributions targeting the identification and the measurement of knowledge spillovers in the past decades. The broad scope of the different approaches has produced important results for the knowledge spillovers identification issue. Thanks to growing theoretical efforts, several key issues have emerged. First, knowledge spillovers entail a spatial dimension that holds notwithstanding globalization and information and communication technology. Second, the spatiality of knowledge spillovers implies patterns of local interactions with situational elements that can contribute to explain observed heterogeneity in innovation paths. However, it is noted that the fast-changing nature of innovation is constantly stimulating the existing literature, posing challenges to established results in the light of rising technological changes, such as blockchain and reverse innovation. Moreover, intensifying trends in socio-economic outlooks, as growing cultural diversity and the consequences on knowledge bases, social networks and market opportunities, are opening new questions on knowledge spillovers dynamics.