This question is of key importance given that maintaining international peace and security is what the Charter of the United Nations defines as the organisation’s primary objective. The article constitutes an original interpretation of the prohibition of the use of force included in the Charter of the United Nations. Article 55 in Chapter IX : International Economic and Social Co-operation speaks of peace in the positive sense, that is not limited solely to the absence of conflicts but rooted in peaceful and friendly cooperation between nations. Peace in the negative sense means only the absence of armed conflicts. This concept of peace is predominant in the UN Charter, having legal and institutional guarantees. The legal guarantee is set out in Article 2 Section 4, which radically restricts the right of states to use force in international relations. The role of the institutional guarantee is played by the Security Council. Its task consists in preserving and restoring international security and peace, and its competences are determined in Chapter VII. Article 51 of the same Chapter, in turn, which provides for a state’s inherent right of individual or collective self-defence. Does the UN Charter prohibit war? The word ‘war’ as such is used in the Charter only once, in the Preamble, where war is condemned. But violence has not disappeared from international relations since the UN Charter’s entry into force. The author presents three ways to interpret Article 2 Section 4 of the UN Charter : integrist, nihilistic and pragmatic. The traditional, integrist interpretation assumes a universal and absolute ban on the use of force in international relations ; the nihilistic interpretation assumes realistic evaluation of the situation, in practice granting numerous exceptions from the prohibition of the use of force. The author himself advocates the pragmatic interpretation, where the text of the norm is interpreted in the context of specific events that bring about the use of force. The application of Article 2 Section 4 involves certain problems : the ban concerns only states, while non-state actors increasingly often use force in international relations as well. Other issues concern the interpretation of the threat of using force, restrictions to the application of the prohibition of the use of force, using force for implementing the principle of responsibility to protect and using force upon consent of the Security Council. The author separately focuses on the inherent right of individual or collective self-defence, provided for in Article 51 of the Charter. The majority of experts in the field represent the view that self-defence is an exception from the principle of using force only in the case of armed aggression of one state against another. The article further highlights the division between functional and structural self-defence. In the conclusion, the author points out the need for the UN Charter to be more open, flexible and intelligent as regards the prohibition of the use of force.