A sentence is a decree of punishment. In law, a sentence forms the final explicit act of a judge-ruled process, and also the symbolic principal act connected to his function. The sentence can generally involve a decree of imprisonment, a fine and/or other punishments against a defendant convicted of a crime. Those imprisoned for multiple crimes will serve a consecutive sentence (in which the period of imprisonment equals the sum of all the sentences), a concurrent sentence (in which the period of imprisonment equals the length of the longest sentence), or somewhere in between, sometimes subject to a cap. If a sentence gets reduced to a less harsh punishment, then the sentence is said to have been "mitigated" or "commuted". Rarely (depending on circumstances) murder charges are "mitigated" and reduced to manslaughter charges. However, in certain legal systems, a defendant may be punished beyond the terms of the sentence, e.g. social stigma, loss of governmental benefits, or, collectively, the collateral consequences of criminal charges.

Statutes often specify the range of penalties that can be imposed for various offenses, and sentencing guidelines sometimes regulate what punishment within those ranges can be imposed given a certain set of offense and offender characteristics. However, in some jurisdictions, prosecutors have great influence over the punishments actually handed down, by virtue of their discretion to decide what offenses to charge the offender with and what facts they will seek to prove or to ask the defendant to stipulate to in a plea agreement. It has been argued that legislators have an incentive to enact tougher sentences than even they would like to see applied to the typical defendant, since they recognize that the blame for an inadequate sentencing range to handle a particular egregious crime would fall upon legislators, but the blame for excessive punishments would fall upon prosecutors.

Sentencing law sometimes includes "cliffs" that result in much stiffer penalties when certain facts apply. For instance, an armed career criminal or habitual offender law may subject a defendant to a significant increase in his sentence if he commits a third offense of a certain kind. This makes it difficult for fine gradations in punishments to be achieved.