This dissertation examines the ways in which three focal high school teachers of second language (L2) French and Spanish in California construct and enact their professional identities as multilingual subjects with diverse linguistic repertoires. By drawing from multiple disciplines, including sociolinguistics, psychology, and education, I examine how social and biographical factors influence language learning and teaching and also how language instructors participate in the construction of the social contexts of language acquisition. Specifically, I explore how L2 teachers of French and Spanish negotiate the impact of social structures on their language use and instruction, including their formal training, personal experiences in the target languages and cultures, and professional responsibilities in highly structured educational institutions. The dissertation concludes with several implications for theory and practice. Building on those, I propose that language teachers’ support networks¬—academic, pre-service, and in-service—incorporate foreign language teachers’ linguistic histories and beliefs about language learning into formal opportunities for professional reflection and dialogue.