An arbitration agreement expresses the consent of the parties to a legal relationship to submit the settlement of their disputes to an arbitral tribunal. As such, it is a unique type of contractual arrangement. While it has a contractual origin, it also confers the arbitral tribunal a jurisdictional power to settle legal disputes which would otherwise be submitted to State courts, hence bearing jurisdictional effects. This dual nature is further demonstrated by the variety of rules governing arbitration agreements, mainly contracts and procedural law, to such extent that it is a commonplace to assert nowadays that arbitration is dual or sui generis. These two aspects further need to be assessed by taking into account the unique legal framework enacted over the years to safeguard or limit the legal effects of arbitration agreements. This Chapter further dives into the sui generis nature of arbitration agreements and the dialectical tension between the contractual and jurisdictional aspects of arbitration as a dispute settlement mechanism. While the validity and applicability of arbitration agreements, mostly inspired by contracts law and the principle of party autonomy, determine the arbitrators’ jurisdiction, the legal mechanisms triggered by arbitration agreements are mainly focused on safeguarding the arbitral tribunal’s jurisdiction.