IPP stands for Imprisonment for Public Protection. It was a type of indeterminate sentence introduced in England and Wales by the Criminal Justice Act 2003 and started to be used in April 2005. IPPs were designed to protect the public from dangerous offenders who were not given a life sentence but were considered too risky to be released at the end of their fixed-term sentence. Offenders sentenced to an IPP were set a minimum term (tariff) which they must spend in prison. After they completed their tariff, they could apply to the Parole Board for release. The Parole Board would release an offender only if it was satisfied that it was no longer necessary for the protection of the public for the offender to be confined. If offenders were given parole, they would be on supervised licence for at least 10 years.

Although IPP sentences were abolished for offenders convicted on or after 3 December 2012, thousands of people subject to such a sentence are still in prison. IPPs have proved difficult to understand and have led to inconsistent sentencing. They have been given to some offenders, while others who have committed similar crimes have served fixed sentences. IPPs have been criticized for being unfair and for leaving victims and their families uncertain about how and when an offender will be released.