The knowledge sciences field has long recognized the importance of communities of practice to the flow of knowledge and situational learning. However, the literature and research has focused mainly on communities in formal organizational contexts. This constraint has limited research and exploration and exposed only a small portion of the knowledge of communities of practice. Focusing only on organizational communities of practice further restricts what we have learned about the full range of knowledge capabilities. The Knowledge of Communities provides an inclusive and comprehensive conceptual framework for understanding the spectrum of communities of practice and their relationship to the development of knowledge capital. Presenting a core standpoint that incorporates the variant perspectives of community processes from social sciences, psychology, behavioral sciences, communication and economics, the authors review existing research, identifying areas where additional work is needed, and present the results as a practical field guide for managers that can be utilized for analyzing any community of practice.