This study investigates the effectiveness in delivering social services of interim housing programs compared to shelters. Interim housing programs represent a new approach to housing and serving homeless adults, one which provides emergency housing in apartment-like units, and in which use of services is voluntary. Shelters tend to provide congregate care and to expect or rely on clients to access needed services in order to secure resources required to obtain housing. Analyses of original survey data, which correct for sample selection utilizing propensity scores, suggest that clients in interim housing programs obtain more professional, advocacy, and employment services than do clients in shelters. This differential service use is found to reflect not client incentives, but the service offerings and referrals made by the programs. In general, the findings suggest that interim housing programs hold particular promise in service rich environments. They also suggest that program contingencies are more important than certain individual client incentives in affecting service use. Finally, the results begin to suggest the value of this new, interim housing-based approach.