The authors analyze and compare three models of innovative knowledge communities: Nonaka and Takeuchi's model of knowledge-creation, Engestrom's model of expansive learning, and Bereiter's model of knowledge building. Despite basic differences, these models have pertinent features in common: Most fundamentally, they emphasize dynamic processes for transforming prevailing knowledge and practices. Beyond characterizing learning as knowledge acquisition (the acquisition metaphor) and as participation in a social community (the participation metaphor), the authors of this article distinguish a third aspect: learning (and intelligent activity in general) as knowledge creation (the knowledge-creation metaphor). This approach focuses on investigating mediated processes of knowledge creation that have become especially important in a knowledge society. (Contains 1 table and 1 note.)