The .NET Framework is a widely used system component for MicrosoftWindows. This thesis describes how the functionality of the framework canbe adapted to Microsoft Excel. Specific operations, such as integration ofuser interfaces, database connections and the ability to divide programs intosmaller components, are discussed. A number of architectural - and designpatterns to facilitate development are analysed.Several techniques have been made up in consultation with experiencedprogrammers. These techniques were further developed by implementinga number of test programs.The results of the study are a number of standard classes for future usageand a larger pilot project containing most of the analysed functionality..