A key aspect of the acquisition of grammar for second language learners involves learning how to make appropriate connections between grammatical forms and the meanings which they typically signal. We argue that learning form/function mappings involves three interrelated principles. The first is the Given-to-New Principle, where existing world knowledge is exploited as a resource for connecting known or "given" meaning with new form-meaning mappings. The second is the Awareness Principle, which states that discovering new mappings between form and meaning is a process which necessarily involves awareness. The third is the real-operating conditions principle, whereby the process of acquiring form-meaning mappings is not complete until learners are able to practice them in a communicative context and through a primary focus on meaning rather than on form. The challenge for grammar instruction is to create conditions for each of these three principles.