Legal issues involving Native American Indian Tribes and surrounding issues are most frequently associated with federal law. However, state laws and regulations may impact tribes. State governments do not have authority over Indian tribes, unless authorized by Congress, and may regulate only on matters that do not affect tribal interests. Tribal governments are not subservient to state governments and may enact their own laws. Current interactions between Indian tribes and states are non-controversial and signal cooperation between the two, for state and tribal governments often work on issues affecting state-tribal relations, including environmental protection, taxation and trust land issues.