In criminal trials, the insanity efenses are possible defenses by excuse, an affirmative defense by which defendants argue that they should not be held criminally liable for breaking the law, as they were legally insane at the time of the commission of alleged crimes. A defendant attempting such a defense will often be required to first undergo a mental examination. It is important to note that the legal definition of "insane" in this context is quite different from psychiatric definitions of "mentally ill", also that the definition of insanity varies between jurisdictions.