The term sustainability first appeared in the 18th century, in the context of forest management. In more recent times, sustainability came into focus in the 1970s, and the concept of sustainable development was introduced in the 1980s, when the role of sustainability in business began to be considered. In the 1990s, tourism began to be considered as a branch through which the goals of sustainable development can be achieved, and in the year 1995 the first world conference on sustainable tourism was held. At the World Summit on Sustainable Development in 2015, the 2030 Agenda for Sustainable Development was adopted, with three goals dedicated to tourism. These goals are helped to be achieved by the Global Council for Sustainable Tourism, which adopted global standards for sustainable travel and tourism - the GSTC criteria for sustainable destinations. GSTC has its own certification bodies through which it is possible to access the destination certification process. National parks were created with the mission to preserve the natural environment and present it to the public, but the increase in the number of visitors brings new challenges to these efforts. The threat to nature by human activities in national parks is becoming a problem for destinations all over the world, and this paper presents the methods by which the governing bodies of the national parks Pembrokeshire Coast and Phi Phi faced these challenges. Plitvice Lakes National Park is the most visited park in Croatia. With the increase in the number of visitors, the negative impact on nature was noticed, and the leadership of the park implemented sustainability principles and principles promoted through GSTC criteria in the current Management Plan 2019-2028. In 2023, Plitvice Lakes National Park became the first Croatian national park to receive the Green Destinations Award for sustainability.