One outcome of recent progress in educational technology is strong interest in providing effective support for learning in complex and ill-structured domains. We know how to use technology to promote understanding in simpler domains (e.g., orientation information, procedures with minimal-branching, etc.), but we are less sure how to use technology to support understanding in more complex domains (e.g., managing limited resources, understanding environmental impacts, etc.). Such domains are increasingly significant for society. Technology (e.g., collaborative tele-learning, digital repositories, interactive simulations, etc.) can provide conceptually and functionally rich domains for learning. However, this introduces the problem of determining what works in which circumstances and why. Research and development on these matters is reflected in this collection of papers. This research suggests a need to rethink foundational issues in educational philosophy and learning technology. One major theme connecting these papers is the need to address learning in the large - from a more holistic perspective. A second theme concerns the need to take learners where and as they are, integrating technology into effective learning places. Significant and systematic progress in learning support for complex domains demands further attention to these important issues.