Every token of language a child receives as input is also a token of language use: someone using language for some or other purpose. In this chapter we discuss the developmental interactions between formal properties of language and principles of language use, or pragmatics. We discuss three avenues of research. How do pragmatic capacities (quantity implicatures and presuppositions) develop? What can we learn about children’s pragmatic expectations from what sometimes look like grammatical errors (quantifier spreading, scope relations)? How can children leverage their pragmatic knowledge for learning more language (pragmatic bootstrapping, subset problem). The overarching theme is that grammatical development and pragmatic development are intertwined in ways that make studying their interaction especially fruitful.