This paper examines US-COOL, one of the disputes called a trilogy of the cases (along with US-Clove Cigarettes and US-Tuna II) under the Word Trade Organization (WTO)'s Agreement on Technical Barriers to Trade (hereinafter "TBT Agreement"). This case was Article 21.5 (compliance) proceeding under the WTO's Dispute Settlement Understanding, addressing a question whether the United States was compliant with the findings made in the original proceeding. There are two key obligations under the TBT Agreement (i.e., Articles 2.1 and 2.2) and one feature of this case was to interpret and clarify the obligation of Article 2.2 (the necessity requirement). However, the violation of Article 2.2 was not found in this case; there is no case yet finding a violation of Article 2.2. This paper discusses the implications on this point.