In order to explain the trends in the development and farm attributes of Integrated Agriculture-Aquaculture (IAA) systems in the Mekong Delta of Vietnam, a participatory community appraisal and two surveys are carried out in three districts with contrasting fish culture input systems. The first survey, undertaken in December 2002, covers 90 households; the second, held December 2004, covers 80 households. The factors driving changes in the farming systems are the introduction of modern rice varieties, the policy of economic liberalization, market demand, and natural disasters. The principal components of IAA systems in the Mekong Delta which the study examines are the land use intensity, market access, farm diversity, farm inputs, and household income. The study finds that the hard-to-change farm characteristics are the land use intensities of rice, orchard and cash crops. In contrast, the easy-to-change farm characteristics are the number of farm components, the land use intensity of fish ponds, on-farm family labor, off-farm and non-farm income, and farm inputs. The main drivers of the changes over the two years are market demand and a poultry disease outbreak (Avian Influenza). Well-off farmers with good farming practices and enough capital tend to intensify their farming practices, while the poorer farmers tend towards diversification in order to safeguard their livelihood and avoid risks.