Dozens of software systems are classified as knowledge building environments. “Knowledge building environment” has an attractive, 21st century, knowledge society ring to it, but how is a knowledge building environment different from a learning environment, and what makes it an environment rather than a tool? This entry addresses these questions, providing answers that suggest that a fully realized knowledge building environment is substantially different from a learning environment, incorporating different forms of support to accomplish a different level of process, and playing a role in a different kind of education or workplace culture.