In 1970 Congress enacted a federal criminal statue called the RICO or Racketeer Influenced and Corrupt Organization Act in an effort to combat organized criminal activities. It has very broad provisions and has been a valuable tool the government uses in the fight on organized crime.
The act has been used to convict senior mob leaders all over the country. For a conviction to stand under RICO it must be proved that the defendant was a part of a criminal enterprise and that they committed two felonies within a ten year period. Under RICO any criminal transaction that involves the use of the telephone, mail, or any interstate communication in furtherance of a criminal act is a target for prosecution. Say for example that the mail was utilized to help commit a felony, not only is the defendant facing mail fraud charges but now he can be prosecuted under RICO.
The acronym RICO stands for Racketeer Influenced and Corrupt Organization. The law is one that is meant to give law enforcement officials a good way to prosecute members of organized crime organizations (like the Mafia).
Basically, the important thing about this law is that it allows prosecutors to charge someone (notably a mafia boss) witha crime even if he never participated in any specifically illegal actions such as extortion or promotion of prostitution. The idea is that because he is a part of this illegal organization, he is a criminal by that very fact.
This law, then, allows the government to charge and convict people for being members of organized crime groups even if they cannot be proved to have committed any specific crimes.