Climate change mitigation and adaptation efforts are urgently needed across Southeast Asia. The financial sector can play a critical role in supporting countries in their journey toward greater resilience and sustainability, but it must adapt to do so effectively. This report shows that while sustainable finance has experienced widespread expansion, sustainable financial markets remain small and unable to meet the funding needs of ASEAN-5 economies for their various sustainability objectives. In fact, the reach of sustainable financial markets is extremely limited, with a sizeable gap especially for small and medium enterprises. Survey evidence reveals that underlying these patterns are marked gaps in climate-related information, capabilities, and investment opportunities. This report highlights the importance of developing the financial architecture for sustainability in financial markets, with emphasis on improving the information environment.