Prison overcrowding is a social phenomenon occurring when the demand for space in prisons in a jurisdiction exceeds the capacity for prisoners in the place. Prison overcrowding can occur when the rate at which people are incarcerated exceeds the rate at which other prisoners are released or die, thereby freeing up prison space. Courts are sentencing criminal offenders to serve prison time and not utilizing other programs like rehabilitation centers effectively. 
At the end of 2010, United States state and federal correctional facilities housed over 1.6 million inmates. At least seven states are currently at 25% over capacity with the highest being Alabama at 196% and closely followed by Illinois at 144% above maximum capacity. Nineteen states in total are operating above maximum capacity. In 2007, California declared a "state of emergency" with regard to overcrowded prisons. 
Operating prisons over maximum capacity is expensive, and inconvenient and dangerous for both prisoners and employees. Possible problems caused by prison overcrowding include:
- Worsening of prison conditions such as sanitation and failure of basic services such as health care
- Spread of diseases within prisons
- Stress among inmates and staff
- Increased risk of violence and prison riots
Some of the solutions to prison overcrowding focus on increasing prison capacity. This includes the construction of new prisons, and the conversion of space within existing facilities that has been used for other purposes into prison space.
Other solutions that have been employed involve keeping offenders, particularly those who commit non-violent or less violent offenses, out of prison. Alternate forms of sentencing are used, including probation, community service, restitution, diversion programs, and house arrest. Additionally, inmates may become eligible for early release from parole and other credits.Criminal drug addicts can be provided with the appropriate health care needs that they need if they aren't in an overcrowded prison and the courts can make use of rehabilitation centers appropriately.
Technology for tracking criminals outside of prison with smart bracelets continues to evolve and improve. One technology involves using GPS to create a geo-fence to monitor criminals to keep them within a designated area at certain times. This enables criminals to go to work, school, and return home in a controlled manner.
In the United States 1 in nearly 100 American adults are incarcerated  There is a lack of rehabilitation and reentry programs most prisoners have to be on a waiting list for these programs. Drug treatment studies for in-prison populations find that when programs are well-designed, carefully implemented, and utilize effective practices they reduce relapse, reduce criminality, reduce recidivism, reduce inmate misconduct, increase the level of the offender’s stake in societal norms, increase levels of education and employment upon return to the community, improve health and mental health symptoms and conditions, and improve relationships. 
- Prisons in California#Prison growth and overcrowding
- Mandatory sentencing
- List of countries by incarceration rate
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