Actus reus is the act—or the omission or failure to act when there is a duty to act—that comprises the physical elements of the commission of a crime. The actus reus generally must be voluntary bodily movements that constitute a crime.
In contrast, mens rea (meaning “guilty mind”) is the criminal intent element of a crime. It is the intent to commit a crime, or the knowledge that the action, or failure to act when there is a duty to act, will result in the commission of a crime.

In Wisconsin, as in other jurisdictions, the concept of actus reus requires that a defendant must have engaged in a voluntary act, or an omission when there is a legal duty to act, that constitutes the physical elements of a crime. This means that for a person to be found guilty of a crime, it must be shown that they actually performed the actions that are considered criminal, or failed to act when they were legally required to do so. On the other hand, mens rea refers to the mental state of the defendant at the time of the crime. Wisconsin law recognizes that for most crimes, there must be proof of a defendant's criminal intent or knowledge that their actions (or inaction) would lead to the commission of a crime. The specific requirements for actus reus and mens rea can vary depending on the crime, but both elements are typically necessary for a conviction. The statutes of Wisconsin, along with interpretations by Wisconsin courts, provide the framework for how these legal principles are applied in criminal cases.