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 Washington State, criminal conspiracy is defined under RCW 9A.28.040. It is considered a criminal conspiracy when two or more persons agree to commit a crime and at least one of them takes an overt act in furtherance of the agreement. The severity of the punishment for a criminal conspiracy in Washington depends on the crime that the conspirators agreed to commit. For example, if the intended crime was a class A felony, the conspiracy is a class B felony; if the intended crime was a class B felony, the conspiracy is a class C felony; and if the intended crime was a class C felony, the conspiracy is a gross misdemeanor. This aligns with the dual purposes of conspiracy laws: to dismantle the collaborative efforts to commit crimes and to hold accountable those involved in the planning stages of criminal activities, even if they do not participate in the execution of the crime itself. 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 reflect the seriousness with which the legal system treats criminal conspiracies.