Ad hoc networks are widely used in military and other scientific areas. With nodes which can move arbitrarily and connect to any nodes at will, it is impossible for ad hoc network to own a fixed infrastructure. It also has a certain number of characteristics which make the security difficult. Routing is always the most significant part for any networks. One way is to transplant ordinary mechanisms in common networks with some improvement while the other way is to find some other factors such as trust to achieve the objective. This paper conducts survey about trust in MANETs and current research in trust based routing.