Transboundary EIA (TbEIA) is one of the most important techniques to implement principles and rules of international environmental law, because it prevents environmental harm, promotes cooperation among states, and consequently helps avoid conflicts and project delay. Public participation as a center-piece of TbEIA is to promote the transparency and legitimacy of decision-making processes in projects with transboundary effects. Mekong Partnership for Environment (MPE), in collaboration with the Asian Environmental Compliance and Enforcement Network (AECEN) organised the MPE Webinar Series on Public Participation in Transboundary EIA on 15 June 2016, hosted by Dr. Peter King. Over 50 Government officials from the EIA department, CSOs along with other EIA Practitioners across Asia and representatives from development partners registered for this event. This is the third in the MPE Webinar Series designed to provide the Regional Technical Working Group on EIA and other attendees with an opportunity to understand the processes of decision-making on projects with transboundary effects and consider if the adaptation of more transparent, legitimate and active participation approaches can reduce the transboundary impact of projects.