This paper focuses on how the entrance of greater numbers of adults into university classes has changed and should continue to change the methods of teaching. The first part of the paper traces the history of the philosophy of adult education, recounting liberal education theories, progressive theories, behaviorist theories, humanistic approaches, and radical adult education theories. The second part details how the various concepts of adult development advocated by recent researchers such as Houle and Knowles have led to changes in adult education. This section is followed by two sections providing information on adult learning styles and adult critical thinking skills as seen through research in adult education. The final section seeks to apply these principles in the university classroom, suggesting refinements in teaching principles, teaching methodologies, classroom environment, classroom activities, classroom techniques, and student expectations in order to respond to adult students. A five-page bibliography is included in the paper. (KC)