fied simplifying change as a critical criterion for mod-ularizing software. Successful designs are those in which a change can be accommodated by modifying a single module. There is a tacit assumption in most of the literature that once a change has been limited to a single module, the cost of making the change is essential y inconsequential. But modules have com-plexity of their own and are frequently large. Thus, making a change can be expensive, even if limited to a single module. We present a method of decomposing modules into smaller components for the purpose of supporting change. Although similar to the approach of modu-larizing programs described by Parnas, our approach is specific to decomposing modules. It is not intended to replace traditional high level modularization but rather to augment it with a second level of modulari-zation where the standard of information hiding can be relaxed. The goal of the method is to make mod-ules easier to change by decomposing them around smaller design decisions—ideally encoding only one design choice per submodule component, In this paper we show how submodule components can be used to address the issue of change. We also demonstrate how the ability to address change with submodule components is, to a large extent, indepen-dent of the design level modularization. Moreover, we show that, at least in some cases, by using submodule components the choice of high level modularization can itself be changed wit bout having to rewrite large amounts of code. Permission to make digital~ard wpy of part or all of this work for personal or classroom use is granted without fee provided that copies are not made or distributed for profit or commercial advantage, the copyright notice, the title of the publication and its date appear, and notice is given that