Specially designed instruction (SDI) is at the heart of special education. The broad legal definition of SDI allows special educators to customize it for students, but could lead to role ambiguity, particularly in inclusive classes where most students with learning disabilities receive services. To examine interpretations of SDI, we conducted a systematic literature review. We identified 73 relevant documents and conducted a content analysis to determine how authors defined what SDI is, who provides it, where it is provided, and why it is offered. We found that conceptualizations of SDI varied widely across documents, and even contradicted each other at times. We present our findings and discuss implications of them for implementation of SDI in practice.