We address 3 critiques raised by Grossman (2011) of self-report measures of mindfulness and the Mindful Attention Awareness Scale (MAAS) and Mindful Attention Awareness Scale--Adolescent (MAAS-A) in particular. Grossman questioned whether self-report measures actually assess mindfulness, whether the construct of mindfulness can be understood apart from mindfulness training, and whether there is empirical evidence to support the validity of mindfulness measures. In response we discuss established theory that attention (and secondarily meta-awareness) is core to the meaning of mindfulness and is the central feature of the MAAS and MAAS-A. We then argue that mindfulness is an inherent capacity that varies between and within persons and is not, as Grossman claimed, a concept applicable to only a trained few. Further, as assessed by the MAAS and MAAS-A, mindfulness is associated with the same variety of outcomes as mindfulness training is theorized to yield. Finally, we provide considerable evidence that the MAAS and MAAS-A are valid instruments. We conclude that although construct measurement is inevitably imperfect, such efforts are critical to building basic knowledge and refining effective interventions.