In the United States, the modern laws related to criminal conspiracy began to take shape in the late nineteenth century. In the most basic definition, conspiracy is an agreement between two or more persons formed for the purpose of committing a crime. The purpose behind criminalizing conspiracy was twofold: to exercise some control over “inchoate” (i.e., unripe or incomplete) activities, and to punish group behavior that had crime as its object.
The crime of conspiracy is the illegitimate agreement. Although simple to define, the offense presents many difficult problems in further analysis. What is an “agreement”? At what point does it begin? What happens if there are multiple agreements over time, or if a person withdraws from the agreement?