The emergence of "mega-regional" trade agreements has recently become the most significant trade policy issue in the Asia-Pacific. Since 2010, governments in the region have launched negotiations for two new trade agreements: the United States-led Trans-Pacific Partnership (TPP) and the ASEAN-led Regional Comprehensive Economic Partnership (RCEP). Differentiated by their membership, scope and level of ambition, the TPP and RCEP embody competing visions for how the Asia-Pacific trade system should evolve, and regional governments must now make choices over which initiative better serves their economic and political interests. This article explores the trade policy choice posed by these mega-regional trade negotiations, reviewing the evolution of the Asia-Pacific trade system, the recent emergence of the TPP and RCEP, and the competitive dynamics inherent in the development of the two proposals. It argues that four key considerations (trade policy ambition, the role of ASEAN, US-China geopolitical rivalry and defensive concerns) will be of key importance in informing regional governments' decisions as the TPP and RCEP move towards completion in 2015.