Knowledge management has recently emerged as an appealing subject in management literature. Although its history is short, it can benefit greatly from the long history of other related disciplines in building its theories. Innovation, organizational learning, knowledge creation, organizational capability building, technology transfer and network, information technology, organizational behavior, and intellectual capital are the disciplines that have accumulated theories related to knowledge management. This paper first presents a conceptual framework that integrates three dimensions: the characteristics of knowledge (tacit and explicit), knowledge process (acquisition, creation, diffusion, storing, measurement, and application of knowledge), and the unit of analysis (individual, organization, sector, and nation). The conceptual framework produces a number of cells that need to be filled by new theories in order to understand knowledge management better. It then reviews existing theories available in the related disciplines that may be used as building blocks in constructing new theories for these cells. Finally, based on the theories available in other disciplines, the paper suggests a set of future research directions for knowledge management at the level of individual, organization, sector, and nation.