This article describes a series of studies that examine the development of literacy in elementary school Spanish-speaking second-language learners. Findings from the research that addresses our first question-regarding cross-language relationships-indicate that first-language reading skills are related to second-language reading skills, but that children must have first-language literacy in the skill for this relationship to exist; oral proficiency in the first language is not sufficient. In our studies that address the second research questions-bilinguals' early literacy development in kindergarten and first grade-Spanish-instructed bilinguals were more likely than English-instructed bilinguals or English monolinguals to treat diphthongs as 2 units, reflecting the influence of Spanish language instruction on English phonological analysis. Moreover, both English vocabulary and literacy instruction made unique, positive contributions to English spelling, whereas Spanish literacy instruction played a more important role than Spanish vocabulary in the production of Spanish-influenced spelling in English. Only bilingual students in Spanish literacy instruction exhibited Spanish-influenced spelling, indicating a powerful effect of language of literacy instruction. Our findings related to the third question-the role of home literacy and language environment on bilinguals' English and Spanish vocabulary development-suggest that becoming or staying proficient in English does not require parental use of English in the home. Spanish, not English, is the at-risk language for children of Hispanic heritage living in the United States. Students need early instruction in Spanish and home support in that language to become and remain proficient in Spanish.