The overlap of homelessness, drug use, and violence has been well established among indigent women, but high rates of HIV infection and violence continue. In particular, homelessness is a consistent and persistent risk factor for HIV. Low threshold access to housing is one structural intervention which holds much promise as an HIV prevention strategy, particularly for high risk HIV negative women who face greater threat of victimization and exploitation while on the street and are ineligible for HIV serostatus related benefits that facilitate access to housing. However, the complex intersection between housing situation and HIV risk environment for women is currently not well understood. Further, access to housing does not equate to housing stability. More often marginally housed persons migrate between greater and lesser degrees of housing stability by shifting housing situations over the course of days, weeks, and months. Innovative qualitative research methods are most appropriate to a pilot investigation focused on the social and structural characteristics of housing situations as HIV risk environments and housing instability as cumulative risk environment stressor for high risk HIV negative women. We propose a longitudinal, qualitative pilot investigation of 20 marginally housed women recruited from free food programs, shelters, and single room occupancy hotels in San Francisco. Interviews will be at baseline and at one-year follow-up to capture the relationships between housing instability and HIV risk environment in real time. Structural, social, interpersonal, and personal dimensions of HIV risk environments by housing situation (street homeless, publicly sheltered, transitional housed, and permanently housed) and as a result of housing instability will be documented. Results from this pilot data will inform a larger RO1 proposal, with sophisticated ethnographic and epidemiological components and, more immediately, HIV prevention programming, and housing and prevention policies affecting high risk marginally housed women at the local and state levels.