This publication, the first in a series on theory, innovation, and practice in andragogy, is a reproduction of two papers first published in 1971 by Coolie Verner and Catherine V. Davison. The first paper in this booklet explores psychological factors in adult learning and instruction, while the second discusses physiological factors. In the five sections of the first paper, the authors discuss learning and instruction as processes, the stages and conditions of learning and instruction, remembering and forgetting, and tips for designing and managing instruction, and include a list of references. The physiological factors explored in the second paper are the aging process, vision, hearing, learning, and performance (psychomotor skills and verbal communication). Their impact on adult learning is the focus of the study, which also includes a summary and references. (KC)