This paper deals with a specific and rarely studied issue of Bosnia and Herzegovina in the field of international judicial cooperation in criminal matters. This is the common problem of successfully working with declarations to multilateral legal instruments. In view of this, the aim of my presentation is to find better solutions to this problem by identifying and correcting basic mistakes and unjustifiable omissions in making use of such declarations. For this purpose special attention is given, initially, to the hierarchy of legal instruments: domestic law and international agreements. It is well-known that in Civil Law (Continental-European, Latin) countries, international agreements are applicable directly, without any enabling legislation, and override domestic law which contradicts them. The priority of such agreements is indisputable in such countries. Belonging to this group of countries, Bosnia and Herzegovina makes no exception. As a result, where Bosnia and Herzegovina is a Party to some international agreement, it cannot unilaterally change anything in this agreement: either by means of its domestic law or in any other way. However, when the international agreement is a multilateral convention, Bosnia and Herzegovina is in the position to unilaterally modify it. The sole and irreplaceable means to reach this goal is a reservation or in some sense a declaration to the multilateral convention. Nevertheless, there are cases where the legislation of this country has not taken into consideration the inability of its own domestic law to change multilateral conventions. This makes it necessary to discuss those cases and explain the need of resorting to declarations, in particular, for the purpose of producing the desired result.