Criminal acts against life in general are very often challenged in the evidentiary proceedings by the claim from the defense that the perpetrator of the criminal offense acted in self-defense. Self – defense is indispensable in situations where a simultaneous or imminent unlawful attack is repulsed by oneself or another. That is, the reason for the exclusion of illegality is therefore no criminal offense. Also, the attack must be illegal, simultaneous or imminent, while the defense must be indispensable. The main goal of the this work was to explain the concept of self-defense in the Criminal Code and to clarify its significance in both Croatian and international law, to clarify its application and to support it with examples from case law. Also, the aim was to develop the assumptions under which it is applicable within the Croatian criminal justice system. Scientific and professional literature, books, secondary data available on the Internet and examples from case law based on the implementation of the Criminal Code were used for the purpose of better preparation of the final paper. Based on the above, it can be said that the necessary defense in criminal cases is possible in most cases, although, due to the specifics of protected goods and specific types of attacks on the property and the special attitude of the perpetrator to the attack, courts should be more careful in assessing it. It is up to them whether they will accept such understandings in the future or whether they will continue to bypass the often complicated establishment of some facts in such situations, thus creating the impossibility of applying a very important criminal law such as the law of necessary defense.