This paper reviews empirical research that has helped to shape evolving perspectives of immersion education since the introduction of French immersion programs in Montreal more than 40 years ago. Research confirms that French immersion students attain high levels of comprehension abilities and functional levels of communicative ability in production, with shortcomings in accurate and idiomatic expression, lexical variety, and sociolinguistic appropriateness. Shortcomings will be explained in terms of processing constraints that result from an interaction among the structural properties of problematic target features such as verbs, pronouns, and gender; their degree of salience in classroom discourse; and a range of learner-internal factors. Following an argument developed by Lyster (2007) with respect to teaching and learning languages through content, the specific argument put forth in this chapter is that many shortcomings in the second language proficiency of French immersion students could be overcome through instruction that is counterbalanced in a way that more systematically integrates language and content.