Mindfulness, with its roots in ancient Buddhist traditions, is defined as the deliberate focus of attention on the present moment, with a quality of nonjudgment and openheartedness. Mindfulness, as it is taught and practiced, is a dynamic process characterized by noticing when one is not mindful and consciously redirecting noncritical attention back to the present moment. This process has not been captured by widely used mindfulness measures, which instead measure the outcome, or presence/absence of mindfulness (e.g., “I notice the smells and aromas of things,” an item from the Five Facet Mindfulness Questionnaire; FFMQ). The Mindfulness Process Questionnaire (MPQ) was created to address this omission by focusing on the process of noticing mindlessness and responding with mindfulness. In preliminary studies examining the MPQ, the measure demonstrated good psychometric properties in both nonclinical and clinical samples. The MPQ predicted clinically relevant outcomes, beyond variance accounted for by the FFMQ and Mindful Attention Awareness Scale, supporting the unique contribution of this measure compared to existing, outcome-oriented mindfulness questionnaires. Subsequent research expanded on these findings with further evidence of the reliability of the MPQ and its use in a wide range of samples: clinical and nonclinical, meditators and nonmeditators. In summary, preliminary research supports the MPQ as a unique, reliable measure that captures the practice of mindfulness across a range of populations.