In this study, the authors both developed and validated a self-report mind- fulness measure, the Toronto Mindfulness Scale (TMS). In Study 1, partici- pants were individuals with and without meditation experience. Results showed good internal consistency and two factors, Curiosity and Decen- tering. Most of the expected relationships with other constructs were as expected. The TMS scores increased with increasing mindfulness medita- tion experience. In Study 2, criterion and incremental validity of the TMS were investigated on a group of individuals participating in 8-week mindfulness-based stress reduction programs. Results showed that TMS scores increased following treatment, and Decentering scores predicted improvements in clinical outcome. Thus, the TMS is a promising measure of the mindfulness state with good psychometric properties and predic- tive of treatment outcome.