Manslaughter is the unlawful killing or homicide of a human being without the premeditation or malice (malice aforethought) required for the criminal offense of murder.

Many states have two types of manslaughter: (1) voluntary manslaughter—the defendant intended to kill the victim, but did so in self-defense, or in the heat of passion and without premeditation, or the defendant was insane and did not understand that the killing was wrong; and (2) involuntary manslaughter—the defendant negligently or recklessly caused the death of another person—such as when a person is intoxicated while operating a motor vehicle and causes an accident that results in the death of another person.

Some states do not have separate criminal offenses for voluntary and involuntary manslaughter—these states may have the offense of manslaughter and identify certain aggravating factors that may enhance the penalties upon a conviction for manslaughter.

Manslaughter is a felony offense and may be punished by a lengthy prison term. Manslaughter laws are generally located in a state's statutes—often in the penal or criminal code.

In Connecticut, manslaughter is categorized into two main types: first-degree manslaughter and second-degree manslaughter, which align with the general concepts of voluntary and involuntary manslaughter, respectively. First-degree manslaughter (CGS § 53a-55) occurs when a person intends to cause serious physical injury to another person and causes the death of such person or a third person, or when a person acts under the influence of extreme emotional disturbance for which there is a reasonable explanation. This is similar to the concept of voluntary manslaughter. Second-degree manslaughter (CGS § 53a-56), on the other hand, involves situations where the defendant recklessly causes the death of another person, akin to involuntary manslaughter. Additionally, Connecticut recognizes manslaughter with a motor vehicle (CGS § 53a-56b) when a person operates a motor vehicle under the influence of alcohol or drugs and causes the death of another person. Manslaughter in Connecticut is a felony offense, with first-degree manslaughter carrying a more severe penalty than second-degree manslaughter. The specific penalties upon conviction can include substantial prison terms and are detailed in the Connecticut General Statutes.