Research over the past several decades has found support for the beneficial impact of mindfulness practice on psychological health. However, there is little known about what aspects of mindfulness practice are responsible for producing positive results. One proposed factor is “mindfulness practice quality,” defined as the degree to which, during formal mindfulness practice, one is persevering in coming back over and over to their present-moment experience with a sense of acceptance or receptivity. The Practice Quality-Mindfulness scale (PQ-M) is a self-report visual analog measure (from 0–100) that was designed to measure mindfulness practice quality. It has been supported in several studies as a reliable and valid measure of mindfulness practice quality. Factor analysis has supported a two-factor structure: (1) perseverance (returning to the present-moment experience no matter how pleasant or unpleasant) and (2) receptivity (openness and willingness to “turn toward” to what is arising in the moment). Internal consistency reliability across several studies has been acceptable (close to α = 0.70). The PQ-M has also been shown to be predictive of improvements in psychological health and is supported as a mediator between formal practice time and outcomes, suggesting that practice quality is an active ingredient of action in mindfulness practice.