This book is a study about the ecological knowledge, definition and vision toward nature of the Karen communities in 2 villages; Krenagbo village, Tambon Mae Chan, Amphoe Umphang, Tak province and Ja Kae village, Tambon Lai Woe, Amphoe Sangkhlaburi, Kanchanaburi province which are located in Thung Yai Naresuan Wildlife Sanctuary. The roles of the ecological knowledge of the communities to the production system, the natural resources management, the stability of ecological management and the relationship of the communities’ social organization are considered. Moreover, it is to study conditions and factors causing the changes in the knowledge. The study suggests that the ecological knowledge which is very important is the knowledge system of agricultural production under the shifting cultivation system which is diverse and complicated. It integrates the knowledge about the forest, weather, plants, animals and the natural protectors together. The important base of the knowledge is the vision toward the cosmology of the Karen who believe that all living things are under the same universe and are related to each other. Human beings are only a part of the main natural system and nature is protected by something. Thus, human beings cannot dominate and possess nature. What they can do is respectfully also for the utilization of nature for the natural utilization respectively. Furthermore, living under the moral culture is a means to maintain the equilibrium of the relationship between human beings and nature. This knowledge and vision leads the Karen to a sustainable utilization of nature. This book also deals with the government’s power and the development projects causing the changes in the villages caused by government power and influence with the capitalized economic development. The force for change through the school system and through the government’s land tax imposition without the understanding of the villagers’ culture have caused changes in communities’ thoughts and vision toward nature and the relationship between human beings and nature finally affecting the natural resources management system.