We argue that Abduction is useful for the problem of Knowledge Assimilation and use it to study the problems of Belief Revision and Truth Maintenance (TM) associated with the task of assimilating a series of observations Q1,...Qn. The close connection between Abduction and TM shown in [Reiter&de Kleer87] is explored further to provide a non-monotonic extension of ATMS that incorporates a dependency-directed backtracking mechanism thus combining the capabilities of ATMS and Doyle's TMS. This TM system has a well-defined semantics inherited from the semantics for abduction which is defined through a generalization of stable models based on autoepistemic logic.