This dissertation defines and defends the concept of ‘criminal oppression.’ Criminal oppression occurs when people are excluded from full participation in important social and political institutions because they are perceived to have violated certain community norms. Oppression is primarily a structural phenomenon, in which practices of formal and informal institutions unjustly harm people based on group membership. In structural oppression, there is rarely an individual who can be said to be responsible for the oppression, but I argue that at times, individuals may also be agents of oppression when they create, perpetuate, or exacerbate structural oppression. Applying this theory of oppression, the criminal justice system in the United States is an oppressive structure that unjustly harms those considered to be ‘criminals’ through a variety of practices. There are three categories of unjust practices: policing, adjudication and punishment, and collateral effects of arrest and conviction. These three categories of practices create the social group ‘criminals’ by subjecting certain people to these kinds of treatments. I use the word ‘criminal’ to describe those who are treated as criminals by police, the courts, and even private individuals like employers. To be a ‘criminal,’ it is not necessary that one has committed a crime or been convicted of a crime. Racial and criminal oppression deeply related historically and conceptually. Nevertheless, they are distinct kinds of oppression. In the United States, those who are not racially oppressed but are ‘criminals’ face many of the same unjust obstacles as those who are racially oppressed in addition to being ‘criminals.’ Some may argue that ‘criminals’ duly convicted of crimes deserve to be socially and politically excluded. But, I argue that the criminal justice system is not properly conceived of as an apolitical institution that can assess moral blameworthiness. Nor should it be able to offer punishments that amount to social and political exclusion. Instead, the criminal justice system is one political institution amongst many, and it ought to be governed by the same principles of liberty and equality that govern other political institutions. Criminal law’s proper function is to facilitate government as a system social cooperation. Therefore, it ought to respond to criminal acts with actions designed to promote inclusion rather than exclusion. Moreover, even if someone has committed a crime, that does not mean that they ought to be subject to violence or permanent second-class status. Finally, I address specific, feminism-driven arguments for using the criminal justice system to fight violence against women. Some feminists argue that the expressivist function of punishment—the ability of punishment to express disapproval and disavowal—makes it a perfect tool for fighting the normalization of violence against women. The problem, they contend, is that this violence is under-punished in the United States, and the solution to ending violence against women is to increase prosecutions and advocate for harsher punishments because punishment will change the social norms and make violence against women rarer. To this, I argue that those who create laws or mete out punishments do not have control over the social meaning of punishment with precision. The historical and present-day oppressive features of criminal law and punishment interfere with the ability of prosecution and punishment to condemn certain types of acts without also condemning people. Thus, feminists who try to use the criminal justice system to fight gender-based violence will find it to be ineffective and potentially harmful to the already oppressed group of ‘criminals.” Chapter 1argues that ‘criminals’ are oppressed using a structural model of oppression that focuses on how collections of institutional policies and practices can create and maintain unjust power relations between groups of people. I will also use an externalist theory of group identity to argue that being arrested or convicted of a crime is not necessary or sufficient for membership in the social group ‘criminal.’ Chapter 2 explains the relationship between racial oppression and the oppression of ‘criminals,’ noting the historical development of the modern prison system. Chapter 3 argues that the proper role of criminal law is to support systems of social cooperation, not to punish pre-political wrongs. I will suggest that criminal law is in essence part of the social contract, not a separate sphere of justice to which distinctive, retributive principles apply. Instead, the criminal law cannot determine moral blameworthiness and is only justified in sanctioning rule violations for the sake of supporting social cooperation in a society whose institutions are worth supporting. In Chapter 4, I propose a feminist, expressivist defense of the use of prosecution and harsh punishment as a response to rape and domestic violence that takes the structural nature of violence against women into account. Chapter 5, however, demonstrates why even this theory cannot justify incarceration in the non-ideal sphere because of the oppressive history and practice of the American criminal justice system.