Conspiracies are among the most common charges brought against individuals in federal criminal prosecutions.  When there are a number of defendants in an indictment, you can expect to see that Count One is a conspiracy charge, whether its brought under the general conspiracy statute (18 U.S.C. § 371) or under a more specific statute, such as mail, wire, or bank fraud conspiracy (18 U.S.C. § 1349), drug conspiracy (21 U.S.C. § 846), or antitrust conspiracy (15 U.S.C. § 1).

Generally speaking, a conspiracy is a "meeting of the minds" to commit a criminal act. In other words, if Person A and Person B get together and discuss committing a crime, that's a conspiracy.  There is a slight twist, however. 

The general conspiracy statute (18 U.S.C. § 371) states:

If two or more persons conspire either to commit any offense against the United States, or to defraud the United States, or any agency thereof in any manner or for any purpose, and one or more of such persons do any act to effect the object of the conspiracy, each shall be fined under this title or imprisoned not more than five years, or both.

If, however, the offense, the commission of which is the object of the conspiracy, is a misdemeanor only, the punishment for such conspiracy shall not exceed the maximum punishment provided for such misdemeanor.

Notice that with this statute, there is an overt act requirement.  In other words, mere meeting of the minds is not sufficient for a conviction under section 371; the actors must make some sort of overt act in furtherance of the conspiracy.

In most other conspiracies, including antitrust conspiracies, the overt act requirement is nowhere to be found, and courts have declined to read the additional requirement into the statutes.  For example:

18 U.S.C. § 1349
Any person who attempts or conspires to commit any offense under this chapter shall be subject to the same penalties as those prescribed for the offense, the commission of which was the object of the attempt or conspiracy.

21 U.S.C. § 846
Any person who attempts or conspires to commit any offense defined in this subchapter shall be subject to the same penalties as those prescribed for the offense, the commission of which was the object of the attempt or conspiracy.

15 U.S.C. § 1
Every contract, combination in the form of trust or otherwise, or conspiracy, in restraint of trade or commerce among the several States, or with foreign nations, is declared to be illegal....

Thus, there is no overt act requirement in fraud or drug conspiracies.  While this is, most of the time, not much of an issue because the federal government is happy to show overt acts that support the charges, it does happen occasionally that there are no overt acts in furtherance of the conspiracy and yet, nonetheless, there will be a conviction.

The other very important thing to understand about federal conspiracies is that the lowest punishment is found in the general conspiracy statute: up to 5 years, a fine, or both.  In every other conspiracy statute, the punishment is the same as if the crime had actually been committed.  Thus, wire fraud conspiracy is punished by up to 20 years in prison (30 if a bank is involved), a fine, or both; and antitrust conspiracy is punished by up to 10 years in prision, a fine of up to $1,000,000 ($100,000,000 if committed by a corporation) or both.

Therefore, there is a tendency to downplay the seriousness of a conspiracy charge, and that would be a mistake.  If you are charged with conspiracy, it is very important to make sure you have an attorney who is familiar with and has had substantial experience in federal courts.