Zen students described their experiences when working with koans, and a phenomenological method was used to identify the structure of those experiences. Zen koans are statements or stories developed in China and Japan by Zen masters in order to help students transform their conscious awareness of the world. Eight participants including 3 females and 5 males from Southern California with 1 to 30 years of experience in Zen answered open-ended questions about koan practice in one tape-recorded session for each participant. Reflection yielded the following thematic clusters: (a) motivation, (b) approaches to working with koans, (c) experiences while working with koans, (d) experiences of insight into koans, (e) working with a teacher, and (f) transformation. Participants described positive transformations including better control of emotions and concentration, better awareness of prejudices and biases with the ability to suppress those types of habitual associations, and a new relation to and acceptance of spiritual questions and doubts.