Language endangerment and loss is a longstanding phenomenon affecting both non-contact languages and contact languages, but contact languages are particularly susceptible. This endangerment has greatly increased and sped up in the last century. Case studies of several languages in China and Thailand show that structural change is often more rapid during language shift. Tujia has been receding for millennia in central China; Gong may have originated during contact between speakers of a variety of Burmese and several local languages in western Thailand several hundred years ago. Several small groups in western China speak languages developed in contact between speakers of Mongolic languages, Tibetan, and Chinese in western China in garrisons set up from about 700 years ago on. The final part of this chapter discusses how communities may be assisted to react to the endangerment of their language. While linguists can document a language, it is only the speakers and the community who can decide and act to maintain it. Some of the problems leading to endangerment and the strategies to overcome them are briefly discussed.