This "Policy Guidance Manual on Wastewater Management With a Special Emphasis on Decentralized Wastewater Treatment Systems (DEWATS)" has been developed based on experience of the policy makers and in consultations with relevant stakeholders at country and regional level and was shared in its signal version to the regional workshop on Wastewater Management and Sanitation on 2-3 April 2015. It is presenting a set of policy recommendations developed during the implementation of the joint ESCAP-UN-Habitat-AIT project on “Strengthening capacity of policymakers in South-East Asia to promote policies and developing plans for improved wastewater treatment and reuse in urban and peri-urban areas,” to address wastewater and sanitation issues through promotion of DEWATS. Cambodia, Lao People’s Democratic Republic, Viet Nam have been selected to conduct national activities including policy studies, national workshops for capacity building and a pilot project. The Manual provides a step-by-step guide on development and implementation DEWATS in developing countries of the region with a set of financial schemes, market opportunities, investment and potential impacts. It is emphasizing the importance of the leading role of Governments in development of norms and policy frameworks and in operationalization of the practical tools to enable business cases. It also addressing the active roles of the communities and private sector in wastewater management and sanitation, with a special emphasis to promote DEWATS.