Force majeure clauses are one of the mechanisms commonly used by the parties in complex and long-term agreements to regulate the effects of supervening circumstances on the obligations of one or both parties. However, there are still issues that have not been sufficiently studied by the doctrine. This paper intends to deal with some of the most relevant ones. In particular, it will analyze the problems related to the faculty of the parties to alter the legal concept of force majeure, the conventional enumeration of events constituting force majeure and, finally, the effects of force majeure on the obligations of the debtor.