Despite the rapid expansion of sustainability science in recent decades, sustainability crises have continued to grow. Sustainability researchers argue that this is partly the result of neglecting people’s inner worlds and call for a stronger consideration of inner states and processes in sustainability scholarship. We argue that the advancement of personal sustainability science, i.e., the systematic inquiry of inner worlds in relation to sustainability, is currently impeded by at least two unresolved issues. First, attitudes, emotions, values, and the like have frequently been the object of sustainability-related research. It thus remains unclear to what exactly researchers should more closely look at when inquiring into people’s inner worlds. Second, the epistemological and methodological foundations for conducting research on inner worlds remain underdeveloped. We illustrate that current research activities usually remain at a phenomenologically shallow level. In response to these issues, we provide conceptual, methodological, and normative cornerstones for a first-person inquiry within personal sustainability science, allowing for an in-depth understanding and potentially even a transformation of people’s inner worlds with regard to sustainability. Overall, we suggest redirecting personal sustainability science more strongly toward the inquiry into people’s subjective (i.e., first-person) experiences of inner states and processes unfolding in relation to sustainability.