Science has greatly enhanced what we know about reading and writing. Drawing on this knowledge, researchers have proffered recommendations for how to teach these two literacy skills. Although such recommendations are aimed at closing the gap between research and practice, they often fail to take into account the reciprocal relation that exists between reading and writing. Writing and writing instruction improve students' reading and vice versa. Theory and evidence that support this reciprocal relation are presented, and implications for the scientific study of reading and writing, policy, and practice are offered, including the proposal that the sciences of reading and writing need to be better integrated.