This paper traces South Korea's history of coastal reclamation from the 1950s until today, exploring how it emerged as the state's program for modernization and economic development and how it has played particular roles in the changing political economy of the country. The developmental state scaled up the size of reclamation practices, significantly extending construction periods and leaving enduring impacts on coastal communities and the marine environment. Large-scale coastal reclamation had been primarily and persistently sought to create agricultural land, of which particular rationales emerged and evolved as the country rapidly industrialized and saw increasing urban-rural disparities. While coastal reclamation is said to have contributed to South Korea's post-war development, it also aided the state's highly uneven spatial economic development strategies by reinforcing the conditions of underdevelopment in rural areas. It had the repeated but temporary effect of politically appeasing rural populations marginalized from sharing in the nation's growing wealth. The agricultural rationales, especially those with an emphasis on rice production, continued to be invented by major reclamation institutions to justify further reclamation. Hailed as a territorial expansion project and promoted for agricultural land conversion through the logic of virtual urban-rural land exchange, the focus of reclamation eventually shifted from rice to land production. Recently as South Korea entered into the stage of post-development, the temporal mismatch between planning and completion found in mega-scale reclamation projects has undermined the initial agricultural land rationale. However, now even land turned flexible to accommodate non-agricultural uses is lacking demand as financial investment in reclaimed land has slowed down. Today, the vacancy of the reclaimed land is actively mobilized in local regionalist politics, once again giving false promises of development to rural populations.