In this closing commentary, I first briefly recognize areas that have made the dialogue between the fields of second language (L2) writing and second language acquisition (SLA) difficult in the past. I then offer some comments on the interfaces that are brought to the fore by the contributions gathered in the special issue. The themes explored are all of an instructional nature, spanning attention to form in writing, written error correction, and individual differences in writing. I close with some additional reflections on the present and future potential for relevant research at the interface between the two fields, specifically calling for the inclusion of teachers, tasks, and L2 proficiency as worthy additional cornerstones of future L2 writing-SLA interface work.