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 Maine, criminal conspiracy is defined under Title 17-A, §151 of the Maine Criminal Code. A criminal conspiracy occurs when a person, with the intent that a crime be committed, agrees with one or more persons to engage in or cause the performance of conduct that constitutes the crime, and an overt act in pursuance of the conspiracy is committed by one of the conspirators. The state of Maine recognizes the seriousness of criminal conspiracies and provides for the prosecution of individuals who plan and attempt to commit crimes, even if the crime itself is not completed. The penalties for conspiracy depend on the classification of the crime that the conspirators agreed to commit. For example, if the target crime is a Class A offense, the conspiracy to commit that crime is a Class B offense. This approach aligns with the dual purposes of conspiracy laws: to dismantle the collaborative efforts to commit crimes and to hold accountable those who contribute to criminal planning. At the federal level, as per 18 U.S.C. §371, individuals involved in a conspiracy to commit an offense against the United States or to defraud the United States can face fines and imprisonment for up to five years. Both state and federal laws emphasize the importance of addressing the preparatory stages of criminal activity, not just the completed acts.