The development and diffusion of environmentally sound technologies (ESTs) are crucial to the implementation of the 2030 Sustainable Development Agenda. This report responds to an interest in facilitating increased trade and investment in ESTs, with a particular focus on renewable energy technologies in the ASEAN region, in line with the 2030 Agenda for Sustainable Development and the Paris Agreement on climate change. The main goal of the report is to identify opportunities and challenges in trade in selected ESTs in ASEAN. To do this, the report analyses regional trade in relation to eight ESTs within four sectors: biomass boilers, solar energy equipment, wind turbines and hydro-electric technology. Further, the report provides a review of national policies and regulatory frameworks in order to improve the understanding of value-chain functioning and regional trade in the ASEAN region in the selected ESTs. Finally, the report offers an in-depth case study of the solar PV industry in Malaysia in order to provide a detailed account of a rapidly emerging sector, both in ASEAN and globally, in terms of trade and investments. Malaysia is a regional production hub in solar PV cells and modules with close trading ties to countries in the ASEAN region and globally. The case study is thus expected to provide deeper insights into the barriers to trade in the national and regional solar PV value chains, which has broader relevance for improving the understanding of the specific factors affecting the trade in ESTs.