Evidence is any testimony, document, physical object or information that a litigant wishes to present in a court of law in an attempt to prove their case. However, in order to be presented before the court, particularly to a jury, evidence must meet three criteria in order to be admissible:
Evidence may only be presented if it will assist the trier of fact in determining the issues underlying the dispute. If evidence will not do this, it is not admissible in that proceeding. For example, evidence of character is generally not admissible as, for the most part, it is merely an attempt to boost or denigrate the credibility of a party. However, where the character of an individual is at issue in a proceeding (such as during criminal sentencing, or during an inquiry for admission into a professional body), character evidence is clearly relevant and may be presented.
For the most part, evidence must be shown to be reliable and preferrably any fact will be supported by evidence given by a witness in court. The most common reliabilty rule is the hearsay rule which forbids the introduction of any statement not made in court under oath as evidence of the truth of that statement. However, there are also rules for the introduction of documents, which generally requires that either they be identified by a witness under oath or that they meet other criteria which shows they are likely to be accurate and unmodified.
Otherwise reliable and relevant evidence may be excluded in order to support wider policy grounds. The best known of these rules is privilege which prevents a lawyer from giving testimony regarding anything said to the lawyer by the client without the client's consent. In addition, otherwise reliable evidence that is obtained in violation of the law may often be excluded on the grounds that allowing the use of such evidence in court would encourage further breaches of the law and would bring the administration of justice into disrepute.