Insanity defense is remains an unsolved problem for most of the country’s legal system and including the Indian legal system. Sometimes the criminal’s insanity softens the desire of revenge against the criminal. Law of insanity is basically a legal or lawful aspect and not a clinical or medical aspect. Therefore, it implies that just experiencing from a mental turmoil is not sufficient to prove insanity. In this concept the person who is convicted or the accused has an obligation of proving the defense of insanity with the help of vital evidences. In insanity defense it is assumed that, while committing any crime, the defendant should be having any mental disorder due to which the individual was unfit and not equipe of knowing or understanding the nature of crime, hence making the accused not legally liable of offense, it is essentially used in criminal prosecution. The term insanity defense has a long history and has progressed a lot. McNaughton’s test or McNaughton’s rule came across as the best method that describes insanity defense. This test stressed on "understandability of right and wrong” and "intellectual" but this test neglect the insufficiency to control, enticing drives or impulses. In India Section 84 of The Indian Penal Code, 1860 describes the law of insanity and talks about the provisions. McNaughton’s rule is very similar to Section 84 of Indian Penal Code, 1860. Insanity law helps in understanding the mental position of a person who is insane and grant them exemption from criminal trials and punishment. This study will tell you about the differences between clinical or medical insanity and legal insanity. Further on it will talk about the impact of insanity defense in India. This article will also focus on important judgements given by courts on insanity defense and will briefly discuss on legal procedure of law of insanity defense. There is a desperate need to set up a law across the country to provide for speedy and fair trial on the cases of insanity defense.