- Multilevel theory, research, and methods in organizations: Foundations, extensions, and new directions, Jossey-Bass, (2000)
- Computers in Human Behavior 25(2):360--370 (2009)
- Educational Technology & Society 10(3):106-121 (2007)
- Instructional Science 14(3):293--326 (May 1986)
- Computers & Education 54(4):932-940 (2009)
- RWTH Aachen, Aachen, (2009), ISSN 1613-0073 .
- Adaptive evolutionary information systems, Idea Group, Hershey, (2002)
- Theoretical foundations of learning environments, Routledge, New York, (2000)
- Instructional-design theories and models: a new paradigm of instructional theory, Lawrence Erlbaum Associates, Mahwah, New Jersey, 2nd edition edition, (1999)
- Trends in Cognitive Science 12(4):129-135 (April 2008)
- Educational Measurement: Issues and Practice 25(4):6-20 (2006)
- Knowledge Spaces: Theories, Empirical Research, Applications, Lawrence Erlbaum Associates, Mahwah, NJ, (1999)
- International Journal on E Learning 5(1):75-88 (2006)
- Oxford University Press, New York, (2007)
- Artificial Intelligence 42(1):7-49 (1990)
- Blackwell Pub., Malden, MA, (2004)
- International Encyclopedia of the Social and Behavioral Sciences, 2.2, Pergamon, Oxford, (2004)
- WWW Alt. '04: Proceedings of the 13th international World Wide Web conference on Alternate track papers \& posters, page 104--113. New York, NY, USA, ACM Press, (2004)
- International Journal of Artificial Intelligence in Education (2007)
- Personnel Psychology (2004)


user