The Thomson Reuters Foundation champions economies that are equitable, participatory, and sustainable, with a focus on environmental respect. Impact investing is crucial for addressing social and environmental inequities but remains underutilized in Southeast Asia. To bridge this gap, the Aspen Network of Development Entrepreneurs (ANDE) partnered with TrustLaw, the TRF's global pro bono service, to enhance understanding of local impact investing regulations in 7 different countries in Southeast Asia: Thailand, Vietnam, Singapore, Indonesia, Myanmar, and the Philippines. Special thanks go to A&O Shearman, DFDL, Mayer Brown, MahWengKwai & Associates, and SyCip Salazar Hernandez & Gatmaitan for their pro-bono support. This guide aims to assist social enterprises, incubators, and investors in navigating local regulations and fostering greater investment in regional startups and their social missions.