Since the Antarctic Treaty was negotiated in 1959, it has undergone major substantive legal transformations as it grew into a multifaceted regime known as the Antarctic Treaty system. Many of those transformations stemmed from actions by the principal decision makers, the Antarctic Treaty Consultative Parties (ATCPs), as they adopted new strategies and values alongside binding legal agreements for managing their activities in circumpolar southern waters. This essay examines the evolution of the modern law of the sea and seeks to explain how it embellished (has it at times challenged?) the character, significance and purposes of the Antarctic Treaty.