The Vietnamese Mekong Delta is located in the southern part of the country where the Mekong River runs through before it empties into the East Sea. Saline intrusion is a recurrent problem causing serious risks for agriculture and coastal livelihoods of the majority of people in the Delta. Collective adaptation plays an important role in improving the capacity of rural community to deal with environmental complexities. This research aims to examine how the collective adaptation supports the farmer and institutional adaptation to the conditions of saltwater intrusion in Tra Vinh and Kien Giang provinces. Statistical analysis was used to examine the trend of saltwater intrusion and the change in livelihoods of farmers in the Delta. The result shows the remarkable increase in salinity over the past twenty years. Various forms of adaptation were demonstrated by farmers’ and governments’ efforts in implementing adaptation practices to address salinity. Farmers have changed from rice to shrimp culture either through an intensive or extensive system where it is favorable to local environmental conditions. Meanwhile, local governments have attempted to establish various mechanisms to support collective actions (e.g., cooperative policies). The study highlights the critical role of formal and informal institutions that assist local adaptation processes. Adaptation practices were most pronounced in areas profoundly exposed to salinity impacts. The study suggests that further attention should be given to the establishment of institutional structures and rural social networks and how they are instrumental to collective adaptation.