The key distinction between criminal law and civil or administrative law is that only criminal laws can punish a person with imprisonment or execution. This distinction is critically important because an individual charged with a crime is entitled to several legal protections that are not available in civil or administrative proceedings. Sometimes the distinction is difficult to understand because the nature of the confinement may be the same as one that would usually be imposed by a criminal law. Thus disease control laws that use the jail for quarantine were found to not be criminal laws, nor are mental health laws that allow persons to be confined for life because they were dangerous to self or others. Even laws designed to prevent witnesses from fleeing by confining them in prison and treating them as prisoners were not found to be criminal laws. [Bell v. Wolfish, 441 U.S. 520 (1979) ]

The courts reviewing these laws to determine whether defendants were entitled to criminal law protections looked to the purpose of the law, not the ultimate confinement. If the imprisonment is to punish for past actions, it is a criminal law. If it is to prevent some type of future harm—spreading a communicable disease, endangering others because of mental illness, or leaving the jurisdiction before testifying at trial—then it is a civil law and the defendant is not entitled to full criminal law due process protections. Although the courts tend to make this determination on the stated intent of the law as passed by the legislature, they are sensitive to claims that the legislature is using a civil law to punish without proper safeguards.