This article discusses the volume and the substance of the amendments that have been made to the tax treaties of Indonesia, Malaysia, Singapore, Thailand and Vietnam through the operation of the G20/OECD Multilateral Instrument on Base Erosion and Profit Shifting. Based on their tax policies, it provides context on their positions and on the related outcomes. The article offers some conclusions on the number of treaties of the states concerned that have been affected by this first of its kind multilateral approach, and on the substance of those changes.