Located in southern Dalmatia, Mljet has some of the best-preserved nature among the inhabited Adriatic islands, and the western part was declared a national park in 1960. After World War II, the island faced intensive depopulation and transformation from an agriculture-oriented economy to a service-oriented economy. This chapter investigates the role of tourism in the socioeconomic transformation of the island and the social pressure of tourism on the small local community. The goals were to investigate the role of tourism in demographic processes on Mljet, its impact on the socioeconomic development of the island, and to measure the pressure of tourism on the local community. The research confirmed the significant role of tourism in the island's socioeconomic and demographic transformation, but it also revealed some of the highest levels of social pressure due to tourism in southern Dalmatia, which is not acceptable for a tourism area with a highly-preserved natural environment.