As one of the oldest criminal law institutes, we can talk about the notion of necessary defense as one of the scenarios that overrides breach of legislation. In view of the Croatian Penal Code, with the necessary defense, the notion of extreme necessity appears. The necessary defense constitutes defense which is indispensable to repel, or deflect, a simultaneous or direct imminent unlawful attack. From the definition we can perceive two basic,necessary and imminent elements that must be fulfilled in order to talk about the necessary defense: an attack, which must be simultaneous, directly forthcoming and unlawful, and a defense that must be urgently needed. Also, there are situations in which a necessary defense is limited. In such situation a person has the right to a necessary defense, but to a limited extent. In addition to the restriction of the necessary defense, there is a notion of encroachment where we prominently recognize intensive and extensive excess. We can rightly say it represents one of the most difficult questions in the case-law, as it is an encroachment prompting the defined boundaries between legality and illegality. According to all this, the necessary defense is in the order of the oldest, finely defined and excpetionally important institutes of criminal law, which we can find as one of the most elaborate topics in contemporary scientific articles.