(Supplement PA 89/89002A, pages 54 - 85, not printed, see Appendix D.1-F). PLANKEE is a planner which is able to do re-planning when execution of the original plan has failed. In the report we first summarize the history of planners and then develop an own planner for the blocks world. The planner uses slightly modified ideas from [Sacerdoti 77]. PLANKEE is implemented in KEE+ PLANKEE is extended to be able to re-plan failed plans. A new initial state is asserted wherefrom the new plan should be applied. By associating information from the planning procedure to the operators in the pla, PLANKEE can use this information to do effective re-planning. The information needed for effective re-planning is (1) to divide the operators into different categories and (2) to extend the use of preconditions.