As the homelessness 'crisis' in the United States enters a third decade, few are as adversely affected as persons with serious mental illness. Despite recent evidence favoring a 'housing first' approach, the dominant 'treatment first' approach persists in which individuals must climb a ladder of program requirements before becoming eligible for an apartment of their own. Drawing upon the concept of 'ontological security', this qualitative study examines the subjective meaning of 'home' among 39 persons who were part of a unique urban experiment that provided New York City's homeless mentally ill adults with immediate access to independent housing in the late 1990s. The study design involved purposively sampling from the experimental (housing first) group (N=21) and the control (treatment first) group (N=18) and conducting two life history interviews with each participant. Markers of ontological security-constancy, daily routines, privacy, and having a secure base for identity construction-provided sensitizing concepts for grounded theory analyses designed to also yield emergent, or new, themes. Findings revealed clear evidence of the markers of ontological security among participants living in their own apartments. This study expands upon previous research showing that homeless mentally ill persons are capable of independent living in the community. The emergent theme of 'what's next' questions and uncertainty about the future points to the need to address problems of stigma and social exclusion that extend beyond the minimal achievement of having a 'home'.