The landmass that comprises Malaysia sits atop the Sunda Shelf and is almost surrounded by sea and straits of Southeast Asia. The narrative of this Chapter focuses on the geographical setting and the ocean basin environment. A suite of maps portrays the limits of the gulf, seas, and straits; the nature and quality of the seabed; the climate and marine meteorology over the regional seas; and the coastal morphology and tidal regime of Malaysia. Whilst the limits of the individual bodies of water (seas and straits) have no political significance the information is included in this study solely for the convenience of the user to gain an understanding of the extent of the regional seas and the locality when referring to maritime issues whether they are of a geopolitical intent or socio-economic context.