A criminal suspect who has been charged with or is likely to be charged with a criminal offense may be held on remand in prison if he or she is denied, refused or unable to meet conditions of bail, or is unable to post bail. This may also occur where the court determines that the suspect is at risk of absconding prior to trial, or is otherwise a risk to society. A criminal defendant may also be held in prison while awaiting trial or a trial verdict. If found guilty, a defendant will be convicted and may receive a custodial sentence requiring imprisonment.

Prisons may also be used as a tool of political repression to detain political prisoners, prisoners of conscience and "enemies of the state", particularly by authoritarian regimes. In times of war or conflict, prisoners of war may also be detained in prisons. A prison system is the organizational arrangement of the provision and operation of prisons, and depending on their nature, may invoke a corrections system. Although people have been imprisoned throughout history, they have also regularly been able to perform prison escapes.