This article presents fifteen different design theories from the behaviorism, cognitivism, and humanism schools of psychology. Information about the theories is presented as a response to three research questions. Descriptions and online learning empirical evidence of eight of the theories are illustrated first. Then, descriptions of seven additional design theories which have not yet been researched in connection with online learning are offered. Finally, results from a study that investigates how often online instructors utilize nine of the theories is presented. Conclusions are made in connection to the three research questions, and further research studies related to the topic are suggested.