Confidentiality is traditionally taken as one of the main advantages of arbitration and is often automatically connected with it or it is simply assumed. However, there are lot of questions that remain unsettled. One of key issues is the legal basis of parties’ duty to maintain confidentiality in international commercial arbitration. The aim of this paper is to analyse the legal basis of the parties’ obligation to maintain confidentiality. At present, it is widely accepted that notions privacy and confidentiality have different meanings and the privacy itself does not ensure confidentiality of arbitration. In various jurisdictions, three positions as to what can constitute the legal basis of the parties’ duty to maintain confidentiality occur. First, in some jurisdictions confidentiality is regarded to be the general principle of international commercial arbitration. Secondly, several national regulations of arbitration expressly prescribe the parties’ duty to maintain confidentiality. And finally, other jurisdictions accept the duty only if there is a confidentiality agreement of the parties including to reference to arbitration rules providing for such a duty.