This chapter examines the effects of aquaculture development on the livelihoods of households in two historically and geographically distinct coastal communities in north and south Vietnam. It is shown that the importance of open-access resources for livelihoods increases in line with the poverty and vulnerability of the social group. This increase has occurred at the same time as a decrease in the availability of open-access products because of the privatization of resources associated with aquaculture. Many openaccess resources are accessed illegally or with unofficial access rights and this has implications for livelihood security, since open-access resources have uncertain rights and legislative status, a status that is open to change and frequently subject to privatization. The high capital investment required and the loans necessary to raise that capital are also increasing the vulnerability of the wealthier households involved in aquaculture.