A novel decision method for autoepistemic reasoning is developed. The method is applicable in a general setting, i.e. for an autoepistemic logic based on a given classical logic. It provides a decision method for a tightly grounded form of autoepistemic reasoning based on Lhierarchic expansions as well as for autoepistemic reasoning based on Moore style expansions and N-expansions. Prominent formalizations of nonmonotonic reasoning, such as default logic and circumscription, can be embedded into autoepistemic logic based on Lhierarchic expansions using simple local translations. Hence, the method can serve as a unified reasoning tool for a wide range of forms of nonmonotonic reasoning.