Housing First (HF), which is recognized as an evidence-based practice by the Substance Abuse and Mental Health Services Administration,1 addresses homelessness by offering immediate access to housing while providing ongoing community-based services.2 An important marker of its success has been increased housing stability and retention rates. Randomized controlled trials have found housing stability and retention for HF participants to be between 73% and 80% as compared to usual care, which, depending on the study consisted of access to existing forms of housing assistance and support in the community or programs following a Btreatment first^ approach that made access to permanent housing conditional on successful treatment adherence, had rates of approximately 30%.2, 3 Furthermore, there has been remarkable consistency across evaluations of HF programs. In a review of eight published studies of Housing First that reported on housing retention and stability during periods that ranged from 1 to 5 years, rates varied from 73% to 88%.4 Despite or perhaps because of these consistent positive housing outcomes, there has been limited discussion of differences in the operationalization of housing stability and housing retention in studies of HF, which reflects inconsistencies in the definition of these concepts in the broader body of research on homelessness and housing.5 For example, Tsemberis et al.2 measured housing stability as Bthe proportion of time spent in stable housing,^ which could refer to living arrangements other than the apartment provided by the HF agency. Aubry et al.6 considered housing stability to be Bdefined as living in one’s own room, apartment, or house or with family for an expected duration of at least six months or having tenancy rights (holding a lease to the housing).^ Collins et al.7 measured both whether a person maintained residency during the 2 years after they moved into a specific HF project building and Bthe number of days they spent continuously housed during the 2 years.^ Yet, as Pearson et al.8 explained, housing stability is Ban iterative process^ that may include loss of housing and changes in residential address. This perspective underscores the potential importance of residential relocations as a critical dimension by which to evaluate and understand housing stability among HF tenants.