The present study investigates the degree to which social, experiential and usage-related factors correlate with Spanish linguistic competence among adult Hispanic Heritage Language (HL) speakers in the United States. Two online survey instruments were developed in furtherance of this research aim: a Likert-scale survey measuring five areas of Spanish usage and experience (time in Spanish-speaking countries (monolingual environment); formal education in Spanish; usage with family; usage with peers; and media usage) and a performance measure focusing on six areas of Spanish grammar that prior linguistic research has identified where the competence of Spanish HL bilinguals in the US may differ significantly from that of the monolingual standard. The reliability and validity of surveys as indicators or predictors of heritage language proficiencies is of both theoretical and practical interest to researchers in the areas of bilingualism, language shift, language contact and loss, and language acquisition. This study incorporated a much larger sample size (N=453) than previous survey or questionnaire-based research in these areas, which in turn permitted the use of more sophisticated statistical and psychometric analytic methods than had previously been implemented. The results indicated that the basic psychometric functioning of the survey instrument was sound, particularly with respect to the three largest subscales. Multiple regression analyses showed that the set of survey subscale scores accounted for a significant portion (19%) of score variance on the morphosyntax measure. The factor most associated with grammatical competence (as determined by the performance measure) was the proportion of Spanish usage with family members not of the respondent's generation (i.e. parents and grandparents) and the single strongest individual predictor was proportion of use with one's mother or stepmother. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com/en-US/products/dissertations/individuals.shtml.]