The authors used Iranian (N = 723) and American (N = 900) samples to develop an Integrative Self-Knowledge Scale for measuring a temporally integrated understanding of processes within the self. They administered this new instrument, the Mindfulness Scale (K. W. Brown & R. M. Ryan, 2003), the Reflective and Experiential Self-Knowledge Scales (N. Ghorbani, M. N. Bing, P. J. Watson, H. R. Davison, & D. L. Lebreton, 2003), and additional sample-specific measures to 3 separate groups of university students in each society. The Integrative Self-Knowledge Scale displayed internal reliability and measurement equivalence, along with convergent, criterion, discriminant, and incremental validity. This new instrument may be useful in promoting cross-cultural research in positive psychology.