Terrorists, drug traffickers, mafia members, and corrupt corporate executives have one thing in common: most are conspirators subject to federal prosecution. Federal conspiracy laws rest on the belief that criminal schemes are equally or more reprehensible than are the substantive offenses to which they are devoted. The Supreme Court has explained that a "collective criminal agreement—[a] partnership in crime—presents a greater potential threat to the public than individual delicts. Concerted action both increases the likelihood that the criminal object will be successfully attained and decreases the probability that the individuals involved will depart from their path of criminality." Moreover, observed the Court, "[g]roup association for criminal purposes often, if not normally, makes possible the attainment of ends more complex than those which one criminal could accomplish. Nor is the danger of a conspiratorial group limited to the particular end toward which it has embarked." Finally, "[c]ombination in crime makes more likely the commission of crimes unrelated to the original purpose for which the group was formed." In sum, "the danger which a conspiracy generates is not confined to the substantive offense which is the immediate aim of the enterprise." Congress and the courts have fashioned federal conspiracy law accordingly. The United States Code contains dozens of criminal conspiracy statutes. One, 18 U.S.C. 371, outlaws conspiracy to commit any other federal crime. The others outlaw conspiracy to commit some specific form of misconduct, ranging from civil rights violations to drug trafficking. Conspiracy is a separate offense under most of these statutes, regardless of whether conspiracy accomplishes its objective. The various conspiracy statutes, however, differ in several other respects. Section 371 and a few others require at least one conspirator to take some affirmative step in furtherance of the scheme. Most have no such explicit overt act requirement. Section 371 has two prongs. One outlaws conspiracy to commit a federal offense; a second, conspiracy to defraud the United States. Section 371 conspiracy to commit a federal crime requires that the underlying misconduct be a federal crime. Section 371 conspiracy to defraud the United States and a few others have no such prerequisite. Section 371 conspiracies are punishable by imprisonment for not more than five years. Elsewhere, conspirators often face more severe penalties. These differences aside, federal conspiracy statutes share much common ground because Congress decided they should. As the Court observed in Salinas , "When Congress uses well-settled terminology of criminal law, its words are presumed to have their ordinary meaning and definition. [When] [t]he relevant statutory phrase is 'to conspire,' [w]e presume Congress intended to use the term in its conventional sense, and certain well-established principles follow." These principles include the fact that regardless of its statutory setting, every conspiracy has at least two elements: (1) an agreement (2) between two or more persons. Members of the conspiracy are also liable for the foreseeable crimes of their fellows committed in furtherance of the common plot. Moreover, statements by one conspirator are admissible evidence against all. Conspiracies are considered continuing offenses for purposes of the statute of limitations and venue. They are also considered separate offenses for purposes of sentencing and of challenges under the Constitution's ex post facto and double jeopardy clauses. This is a brief discussion of the common features of federal conspiracy law that evolved over the years, with passing references to some of the distinctive features of some of the statutory provisions. There are no one-man conspiracies. At common law where husband and wife were considered one, this meant that the two could not be guilty of conspiracy without the participation of some third person. This is no longer the case. In like manner at common law, corporations could not be charged with a crime. This too is no longer the case. A corporation is criminally liable for the crimes, including conspiracy, committed at least in part for its benefit, by its officers, employees and agents. Moreover, a corporation may be criminally liable for intra-corporate conspiracies, as long as at least two of its officers, employees, or agents are parties to the plot. Notwithstanding the two-party requirement, no co-conspirator need have been tried or even identified, as long as the government produces evidence from which the conspiracy might be inferred. Even the acquittal of a co-conspirator is no defense, although no conviction is possible if all but one alleged conspirator are acquitted. Moreover, a person may conspire for the commission of a crime by a third person though he himself is legally incapable of committing the underlying offense. It is not enough, however, to show that the defendant agreed only with an undercover officer to commit the underlying offense, for there is no agreement on a common purpose in such cases. As has been said, the essence of conspiracy is an agreement, an agreement to commit some act condemned by law either as a separate federal offense or for purposes of the conspiracy statute. The agreement may be evidenced by word or action; that is, the government may prove the existence of the agreement either by direct evidence or by circumstantial evidence from which the agreement may be inferred. The task of sifting agreement from mere association becomes more difficult and more important with the suggestion of overlapping conspiracies. Criminal enterprises may involve one or many conspiracies. Some time ago, the Supreme Court noted that "[t]hieves who dispose of their loot to a single receiver—a single 'fence'—do not by that fact alone become confederates: They may, but it takes more than knowledge that he is a 'fence' to make them such." Whether it is a fence, or a drug dealer, or a money launderer, when several seemingly independent criminal groups share a common point of contact, the question becomes whether they present one overarching conspiracy or several separate conspiracies with a coincidental overlap. In the analogy suggested by the Court, spokes with a common hub need an encompassing rim to function as a wheel. When several criminal enterprises overlap, they are one overarching conspiracy or several overlapping conspiracies depending upon whether they share a single unifying purpose and understanding—one common agreement. In determining whether they are faced with a single conspiracy or a rimless collection of overlapping schemes, the courts will look for "the existence of a common purpose ... (2) interdependence of various elements of the overall play; and (3) overlap among the participants." "Interdependence is present if the activities of a defendant charged with conspiracy facilitated the endeavors of other alleged co-conspirators or facilitated the venture as a whole." If this common agreement exists, it is of no consequence that a particular conspirator joined the plot after its inception as long as he joined it knowingly and voluntarily. Nor does it matter that a defendant does not know all of the details of a scheme or all of its participants, or that his role is relatively minor. Conviction under 18 U.S.C. 371 for conspiracy to commit a substantive offense requires proof that one of the conspirators committed an overt act in furtherance of the conspiracy. More than a few federal statutes, however, have a conspiracy component that does not include an explicit overt act requirement. Whether these statutes have an implicit overt act requirement can be determined only on a statute-by-statute basis. Even there, however, the courts have sometimes reached different conclusions. In the case of prosecution under other federal conspiracy statutes that have no such requirement, the existence of an overt act may be important for evidentiary and procedural reasons. The overt act need not be the substantive crime which is the object of the conspiracy, an element of that offense, or even a crime in its own right. Moreover, a single overt act by any of the conspirators in furtherance of plot will suffice. Federal law contains several statutes that outlaw defrauding the United States. Two of the most commonly prosecuted are 18 U.S.C. 286, which outlaws conspiracy to defraud the United States through the submission of a false claim, and 18 U.S.C. 371, which in addition to conspiracies to violate federal law, outlaws conspiracies to defraud the United States of property or by obstructing the performance of its agencies. Section 371 has an overt act requirement. Section 286 does not. The general principles of federal conspiracy law apply to both. The elements of conspiracy to defraud the United States under 18 U.S.C. 371 are (1) an agreement of two or more persons; (2) to defraud the United States; and (3) an overt act in furtherance of the conspiracy committed by one of the conspirators. The "fraud covered by the statute reaches any conspiracy for the purpose of impairing, obstructing or defeating the lawful functions of any department of the Government" by "deceit, craft or trickery, or at least by means that are dishonest." The plot must be directed against the United States or some federal entity; a scheme to defraud the recipient of federal funds is not sufficient. The scheme may be designed to deprive the United States of money or property, but it need not be so; a plot calculated to frustrate the functions of an entity of the United States will suffice. In contrast, a second federal statute, 18 U.S.C. 286, condemns conspiracies to defraud the United States of money or property through submission of a false claim. The elements of a Section 286 violation are that "the defendant entered into a conspiracy to obtain payment or allowance of a claim against a department or agency of the United States; (2) the claim was false, fictitious, or fraudulent; (3) the defendant knew or was deliberately ignorant of the claim's falsity, fictitiousness, or fraudulence; (4) the defendant knew of the conspiracy and intended to join it; and (5) the defendant voluntarily participated in the conspiracy." Conviction does not require proof of an overt act in furtherance of the conspiracy.