The Trans-Pacific Partnership (TPP) is a proposed regional free trade agreement (FTA) currently under negotiation between Australia, Brunei, Canada, Chile, Malaysia, Mexico, New Zealand, Peru, Singapore, the United States, and Vietnam. The negotiating partners have expressed an interest in allowing this proposed “living agreement” to cover new trade topics and to include new members that are willing to adopt the proposed agreement’s high standards. Canada and Mexico are the most recent countries to join the negotiations and Japan has participated in consultations with the partner countries about the possibility of joining. The TPP negotiations are of significant interest to Congress. Congressional involvement includes consultations with U.S. negotiators on and oversight of the details of the negotiations, and eventual consideration of legislation to implement the final trade agreement. In assessing the TPP negotiations, Members may be interested in understanding the potential economic impact and significance of TPP and the economic characteristics of the other TPP countries as they evaluate the potential impact of the proposed TPP on the U.S. economy and the commercial opportunities for expansion into TPP markets. This report provides a comparative economic analysis of the TPP countries and their economic relations with the United States. It suggests that the TPP negotiating partners encompass great diversity in population, economic development, and trade and investment patterns with the United States. This economic diversity and inclusion of fast-growing emerging markets presents both opportunities and challenges for the United States in achieving a comprehensive and high standard regional FTA among TPP countries.