Interactive systems, such as editors and program development environments, should be explicitly support recovery - facilities that permit a user to reverse the effects of past actions and to restore an object to a prior state. A model for interactive systems is presented that allows recovery to be defined precisely and user and system responsibilities to be delineated. Various implementation techniques for supporting recovery are described. Application of a general recovery facility to support reverse execution is discussed. A program development system (called COPE) with extensive recovery facilities, including reverse execution, is described. Keywords: recovery, reverse execution, undo, checkpoint, editor, programming environments.