A factor analysis of a test battery that included early first-language (L1) achievement, L1 cognitive ability, second-language (L2) aptitude, and L2 affective measures to predict oral and written L2 proficiency was conducted. The analysis yielded 4 factors that were labeled Language Analysis, composed of L1 and L2 language comprehension, grammar, vocabulary, and inductive language learning measures; Phonology/Orthography, composed of L1 and L2 phonemic coding and phonological processing measures; IQ/Memory, composed of L1 intelligence and L2 paired-associate learning measures; and Self-Perceptions of Language Skills, composed of L2 motivation and L2 anxiety measures. The 4 factors explained 76% of the variance in oral and written L2 proficiency. Findings support the view that L2 aptitude is componential. Results are discussed in the context of long-term L1-L2 relationships and individual differences in L2 learning.