<p>This article sets out a phenomenological account of mourning as a ground attunement and proposes that an in-depth analysis of this phenomenon is central to understanding the complex nature of all grief experiences. To support this claim, we begin by highlighting the inherent twofold structure of grief, which encompasses both an ontological and an ontic sense of loss. The ontic sense of loss refers to what is typically associated with grief—the particular loss of a significant relation within a person’s lifeworld. The ontological sense of loss, by contrast, designates a more generalized sense of loss, reflecting the negative grounds of human existence as marked by loss through the existential conditions of vulnerability, transience, and finitude. Building on this distinction, we explore how mourning functions as a ground attunement reflecting the ontological sense of loss. Finally, we illustrate the significance of recognizing mourning as a ground attunement for the analysis of experiences of loss. First, we demonstrate its role as a background attunement in all experiences of loss. Second, we focus on two cases in which mourning becomes foregrounded in experience: (a) mourning one’s own death and (b) ecological mourning. In the concluding remarks, we further reflect on the fundamental role of mourning as not only constitutive of mattering and caring, but maybe even as, as several authors have suggested, a driver for culture itself.</p>