Purpose: This study used structural equation modeling to investigate the dimensionality of language in Spanish-English bilingual kindergartners. Five theoretical models were compared, including (a) a unidimensional model; (b) a two-dimensional model by language (Spanish, English); (c) a three-dimensional model by domain of language (phonology, semantics, morphosyntax); (d) a second-order model organized first by language (Spanish, English), with each language dimension comprising three domain-specific dimensions (phonology, semantics, morphosyntax); and (e) a six-dimensional model with freely covarying language-specific domains. Method: Participants included 238 Spanish-English bilingual kindergartens, as identified by parent report of current language exposure and direct language measures. All participants completed a battery of phonology, semantics, and morphosyntactic test items in English and in Spanish. Results: The six-dimensional covarying model constrained by domain and language provided the best fit for the data, with six separate factors for phonology, morphosyntax, and semantics in English and Spanish. The excellent model fit is supported by findings of a [chi-squared] to df (degrees of freedom) ratio < 2 with no significance, comparative fit index > 0.95, standardized root-mean-square residual < 0.08, and root-mean-square error of approximation values [less than or equal to] 0.05. Conclusions: Results support emergent theories of bilingual language development. Application of the results to the evaluation and intervention of oral language abilities in bilingual children entering the formal education setting are considered.