The connections among language, writing system, and reading are part of what confronts a child in learning to read. We examine these connections in addressing how reading processes adapt to the variety of written language and how writing adapts to language. The first adaptation (reading to writing), as evidenced in behavioral and neuroscience data, is achieved through a universal constraint that language places on writing and through the tuning of reading procedures imposed by specific features of writing systems. Children acquire skill in reading through increasing specialization of procedures tuned to their writing system, while also acquiring more general (universal) procedures that serve language mapping and cognitive control. For the second adaption (writing to language), we present examples from several languages to suggest that writing systems tend to fit their linguistic properties, thus providing adaptive variation in writing-to-language mapping. We suggest that this writing-language fit facilitates the child's learning how his or her writing system works.