Mass incarceration refers to the practice of imprisoning an unusually large percentage of a population, often in ways that disproportionately affect marginalized or disadvantaged groups. While the United Nations does not operate its own penal system, it provides a global framework for how criminal justice systems should function in line with human rights standards. Through various international guidelines and conventions, the UN has consistently raised concerns about the negative consequences of mass incarceration, particularly when it results in overcrowded prisons, excessive pre-trial detention, or the disproportionate imprisonment of poor, minority, or vulnerable communities.

The United Nations views mass incarceration as a serious issue that undermines the principles of justice, equality, and proportionality in sentencing. It has emphasized that incarceration should be used as a last resort and only when necessary to protect society. The UN advocates for alternative sentencing options such as community service, probation, fines, or restorative justice measures, especially for non-violent or minor offences. It encourages countries to address the root causes of crime, including poverty, social exclusion, and lack of education, rather than relying heavily on imprisonment.

Documents such as the United Nations Standard Minimum Rules for the Treatment of Prisoners (known as the Nelson Mandela Rules), the Tokyo Rules on non-custodial measures, and the Bangkok Rules for the treatment of women prisoners highlight the UN's commitment to dignity, fairness, and rehabilitation within the justice system. The UN also warns that mass incarceration can lead to systemic violations of human rights, including degrading conditions of detention, denial of medical care, and the breakdown of family and community ties.

In summary, while the UN does not impose penalties itself, it strongly discourages the practice of mass incarceration and calls on member states to develop justice systems that are fair, humane, and focused on rehabilitation rather than punishment alone.