The geomorphological features of the Lower Mekong Plain and their relationships with floods, as well as the subsurface geology and the major depositional processes in the area, are discussed. From the interpretation of aerial photos and field reconnaissance, the Lower Mekong Plain in Cambodia is characterized as a floodplain with natural levees and back marshes. These geomorphological features influence the extent of the extensive inundation that occurs during every rainy (wet) season. An extreme flood in 2000 confirmed the close relationship between micro-land forms and the flooding. A preliminary study of bore-hole logs in the area of Phnom Penh was also carried out. Base rocks are shallower in the western part, whereas thick (>130 m) Quaternary deposits occur in the eastern part, suggesting the presence of a structural basin.