A criminal conspiracy is generally a partnership formed to commit a crime or crimes. A criminal conspiracy exists when two or more persons form an agreement to violate a law that includes criminal penalties, and then take one or more steps designed to accomplish the goal of the conspiracy.

Federal and state statutes make criminal conspiracies illegal for two primary purposes: (1) to help combat the powerful forces created when two or more people collaborate to commit a crime; and (2) to allow criminal prosecutors (state and federal) to prosecute persons who play a role in planning a crime but who are not involved in the physical acts taken to complete the underlying crime.

For example, under federal law, if two or more persons conspire either to commit any offense against the United States, or to defraud the United States, or any agency of the United States in any manner or for any purpose, and one or more of such persons do any act to accomplish the objective of the conspiracy, each of the conspirators may be fined under and imprisoned for up to five years. See 18 U.S.C. §371. And most states have statutes (usually located in the penal or criminal code) that make criminal conspiracies a crime and include significant punishment upon conviction.

In New Hampshire, criminal conspiracy is defined under RSA 629:3. The statute outlines that a person is guilty of conspiracy if they agree with one or more persons to commit a crime and a participant takes an overt act in furtherance of the conspiracy. The intent to commit the crime is a crucial element of conspiracy. The punishment for conspiracy in New Hampshire depends on the crime that the conspirators agreed to commit. If the intended crime is a misdemeanor, the conspiracy is a misdemeanor as well. If the intended crime is a felony, the conspiracy is punished in accordance with the class of that felony. Federally, under 18 U.S.C. §371, if two or more persons conspire to commit an offense against the United States or to defraud the United States, and any act is taken to achieve the conspiracy's goal, each conspirator may face fines and imprisonment for up to five years. Both state and federal laws against conspiracy aim to deter the collaboration in criminal activities and allow for the prosecution of those involved in the planning stages of a crime, even if they do not participate in the actual commission of the crime.