Impeachment by prior conviction is a legal process in which a witness's testimony in court is rendered invalid due to the witness having previously been convicted of a crime. This form of impeachment is typically used in criminal cases, as it is generally assumed that a witness with a criminal record may be biased or untrustworthy. The two main types of impeachment by prior conviction are direct impeachment and collateral impeachment. Direct impeachment involves introducing evidence of a prior conviction in order to discredit the witness. The conviction must be relevant to the case, and the prior conviction must be for a crime of dishonesty or false statement. This form of impeachment is often used to challenge the credibility of an eyewitness who has provided testimony in a criminal trial. Collateral impeachment involves introducing evidence of a prior conviction in order to challenge the witness's character. This is usually done in order to show that the witness is of bad moral character and therefore unreliable. The prior conviction does not have to be for a crime of dishonesty or false statement; any prior conviction that casts doubt on the witness's character may be used. In both direct and collateral impeachment, the prior conviction must be proven beyond a reasonable doubt. The prior conviction evidence must also be relevant to the case, and must be balanced with any other evidence that may be presented in favor of the witness's credibility.