Optional or unilateral arbitration clauses give the option to one contractual party to choose whether to commence proceedings before a national or arbitral court after the dispute between the parties has already arisen. The party with the option is at an advantage considering that choosing the more favorable dispute resolution method enhances her chances for a successful settlement. This article focuses on the basic features of optional or unilateral arbitration clauses and their position in comparative and domestic law. It analyses American and English court practice, as well as selected German and French cases. It finds that most EU Member States have a positive attitude towards optional arbitration clauses. The author emphasizes the position of German courts which invalidate these clauses if a party with the option wishes to utilize it after the other party has already commenced arbitral or judicial proceedings. Conversely, the author advocates the view that the Croatian courts should give advantage to party autonomy, where it recommends that parties provide for a special procedure when constructing optional arbitration clauses. This procedure should provide for communication between the parties before any proceedings are commenced in order to avoid parallel proceedings. Also, this article finds that, although optional arbitration clauses are rare in the field of capital markets, the Croatian legislature has provided for obligatory use of this type of clauses for disputes between management companies and investors of UCITS funds. Finally, in spite of the fact that there have been no cases before the Croatian courts regarding the validity of optional arbitration clauses, the author is of the opinion that the Croatian courts would take a positive attitude towards these clauses.