Admissible evidence is that evidence which may be received by the judge or jury in a case in order to decide the merits of a controversy. Rules of evidence, which vary by jurisdiction, determine the admissibility of evidence. It is the judge's duty to apply the rules of evidence in the case at hand to determine its admissibility, however, the judge need not introduce all admissible evidence.
For example, evidence which is cumulative (duplicative) of previously introduced evidence may be excluded in the interest of judicial economy. Judges may also exclude evidence when its probative value (tendency to prove the truth or falsity of an issue in controversy) is outweighed by considerations of its prejudicial effect on the passions of the jury, tendency to mislead or confuse the jury, or unwarranted consumption of court time.