According to spiritual traditions, meditation is a way of attention that – if practiced regularly – can lead to deeper levels of consciousness. The development of the MEDI and MEDEQ was guided by the research question of whether meditation depth can be measured validly across different meditation traditions and methods. Forty-five authorized meditation teachers from six different traditions – Yoga, Zen, Theravada Buddhism, Tibetan Buddhism, Christian contemplation, and Taoism – were asked about the depth of different experiences. The agreement was highly significant. Five clusters, interpreted as depth structures, could be found through cluster analysis: “hindrances,” “relaxation,” “concentration,” “essential qualities,” and “non-duality.” Using a separate sample of 122 meditators, an item and factor analysis supported a unidimensional factor called meditation depth. On this basis, the Meditation Depth Questionnaire and its shorter version, the Meditation Depth Index, were constructed. Further studies supported the reliability and validity of the instruments.