It is a Washington federal grand jury which will decide, after secret hearings, if indictments are to be handed down arising from the allegations that President Clinton and his adviser, Mr Vernon Jordan, urged Ms Monica Lewinsky, to cover up an affair she may have had with the President, Joe Carroll reports.
But what are grand juries and what is their role? Basically they study evidence, hear testimony and vote on whether to file charges, called indictments or presentments. No judge is present, the hearings are in secret and the grand jurors - picked from a pool of qualified citizens - and witnesses are usually forbidden to reveal what has occurred.
Grand juries, which usually have 23 members (16 are needed for a quorum and 12 votes for a decision), are a constitutional requirement for inquiries into serious crimes.
The Fifth Amendment to the US Constitution says that "no person shall be held to answer for a capital, or otherwise infamous crime, unless on a presentment or indictment of a Grand Jury".
A "presentment" is the legal term for a charge filed in a case the grand jury has investigated itself. An indictment refers to a case prepared by a prosecutor and submitted to a grand jury.
The Fifth Amendment also allows persons not to have to give evidence which would incriminate them. Persons who "plead the Fifth" can also be granted immunity from prosecution but if they continue to refuse to testify, they can be imprisoned for contempt.