The International Center for Tropical Agriculture (CIAT) collaborated with various research and development partners in nine countries in South and Southeast Asia to document the adoption of different cassava varieties. Cassava experts from Vietnam, Thailand, Cambodia, Laos, Myanmar, The Philippines, Indonesia, China and India got together in country workshops to discuss the use of different cassava varieties and estimated the adoption of these varieties at major production zones and national levels. A variety of disciplines that included breeding, seed production, extension, economics and plant protection contributed to this effort and provided for many countries the first estimates of adoption of this root crop. The more diversity of disciplines and representation of cassava production areas consulted, the more consistent and reliable the estimates we reported. Adoption estimates indicate that out of 4.1 million of hectares of cassava production targeted in the nine countries, 2.7 million (65%) are grown using CIAT related varieties, However, the level of adoption of varieties varies from country to country implying different level of success of different cassava genetic improvement programs in the region.