The series of Asia-Pacific conferences on unsaturated soils began in Singapore in 2000 with a strong emphasis on both the theoretical aspect and practical significance of unsaturated soil mechanics in the region. The conferences have provided a forum for researchers and practitioners in the region and beyond to present their latest developments and exchange ideas in the subject, with strong relevance to problems in the region such as heave/desiccation shrinkage, collapse, rainfall-induced slope instability, contaminant transport, etc. The latest developments in unsaturated soil mechanics will also lead to a much better understanding and solution of many emerging problems such as soil/atmosphere interaction, thermal and chemical influence, and climate change.