His research spans the medieval, early modern, and contemporary periods of Japanese history. Currently he is investigating religion during the Tokugawa period, especially those aspects of Japanese culture associated with manuscripts, printing, secrecy, education, and proselytizing. Although many of his publications focus on Zen Buddhism (especially Soto Zen), he also researches Tendai and Vinaya Buddhist traditions, Shinto, folklore and popular religions, as well as Japanese martial arts and traditional approaches to health and physical culture.