A programmer spends more time modifying already existing programs than constructing original ones. An attempt is made to formulate techniques of program modification, whereby a program that achieves one result can be transformed into a new program that uses the same principles to achieve a different goal. For example, a program that uses the binary search paradigm to divide two numbers may be modified to calculate the square-root of a number in a similar manner.Program debugging is considered as a special case of modification if a program computers wrong results, it must be modified to achieve the intended results The application of abstract program schemata to concrete problems is also viewed from the perspective of modification techniques.We, have embedded this approach in a running implementation; our methods are illustrated with several examples that have been performed by it.