The boundaries of modern tribal criminal jurisdiction are defined by a handful of clear rules—such as a limit on sentence length and a categorical prohibition against prosecuting most non-Indians—and many grey areas in which neither Congress nor the Supreme Court has specifically addressed a particular question. This Article discusses five of the grey areas: whether tribes retain concurrent jurisdiction to prosecute major crimes, whether tribes affected by Public Law 280 retain concurrent jurisdiction to prosecute a full range of crimes, whether tribes may prosecute Indians who are not citizens of any tribe, whether tribes may prosecute their own citizens for crimes that occur outside of Indian country, and how much authority and flexibility tribes have to address juvenile delinquency as they see fit. Many courts have employed an “outside in” approach to these questions, one which begins by assessing the scope of federal and state criminal jurisdiction and then attempts to discern the minimum degree of tribal criminal power necessary to fill the gap left by federal and state authority. Because many tribal criminal justice systems have long devoted most of their resources to filling this gap (prosecuting only minor crimes committed by tribal citizens within Indian country), it may seem to a court that any further exercise of jurisdiction is unnecessary and new, leading to a limited vision of tribes’ retained criminal jurisdiction. This approach prevents engagement with tribal jurisdiction and substantive criminal law on their own terms, leaving courts and legislators to rely on generalizations and assumptions rather than carefully considering the purpose and scope of, and limitations on, tribal criminal jurisdiction. In the past few decades, however, courts have followed the lead of tribes and legal scholars by employing an “inside out” approach, which centers tribes by asking only whether a particular power is an element of tribes’ sovereignty and whether it has been taken away. When a court employs an inside out approach, neither the scope of federal and state jurisdiction nor the common practices of tribal criminal courts bear directly on the scope of modern tribal criminal power. Tribal criminal jurisdiction is examined standing alone, which may lead to consideration of why criminal jurisdiction is necessary for sovereignty, the multiple functions such jurisdiction serves, and the various forms it may take. As applied to the questions discussed here, the result is a much broader vision of tribes’ retained criminal power. This Article explains why the inside out approach is the more appropriate one and how the analytical shift is attributable in large part to the work of Carole Goldberg. By addressing five specific grey areas of tribal jurisdiction, this Article demonstrates how the use of an inside out methodology—a clear alternative to the implicit divestiture approach employed most famously in Oliphant v. Suquamish Indian Tribe—can have significant consequences for the future of tribal criminal jurisdiction.