This chapter argues that the concept of Traditional Ecological Knowlegde means more than the accumulated environmental knowledge and comprehension of natural phenomena. Rather, it is constituted by a set of evolving beliefs and practices that understands its own dynamic relationship with other beings in the environment. The examples of Traditional Ecological Knowledge (TEK) illustrated in this chapter include Apurinã and Manchineri communities in Brazilian Amazonia, and Sámi communities in the Arctic.