This work identifies developmental stages in the acquisition of object pronouns by instructed second language learners of Spanish. It examines learners ranging from beginner to advanced, where the most advanced are themselves teachers of Spanish language courses. Study abroad experience is also a variable in the data. The book explores language production from a functionalist perspective, examining form-to-function and function-to-form mappings. It provides insights into related developments in production, placement and processing of object pronouns. Detailed analysis reveals that the most powerful predictor of performance across levels and within levels for each of these is the level of the learner.Formal instruction and the study abroad experience is examined, both the specific instruction on object pronouns and overall exposure to instruction.