A large and growing body of empirical research shows that social relationships and the networks these relationships constitute are influential in explaining the processes of knowledge creation, diffusion, absorption and use. We refer to such networks as 'knowledge networks.' We advance an understanding of knowledge networks at multiple levels by conducting a systematic review and analysis of empirical research published on this topic in leading management, psychology, sociology and economics journals. We develop a comprehensive framework that organizes the knowledge networks literature, which we use to review extant empirical research within and across multiple disciplines and levels of analysis. We identify points of coherence and conflict in theoretical arguments and empirical results within and across levels and identify emerging themes and promising areas for future research.