The Harris Matrix -formulated by Dr. Edward C. Harris in 1973 -is the established way of representing the archaeological stratigraphy of an excavation. The Harris Matrix is a sequential diagram defining relations between stratigraphic units. It is an important method to document the stratification that is destroyed by the excavation process and hence a vital tool for analysis. Although the Harris Matrix has become a quasi standard of archaeological stratigraphy, only a few software tools exist to create and edit these diagrams. An evaluation of these tools showed that they do not completely comply with the theory or suffer from poor usability. Therefore we decided to develop a new application, called Harris Matrix Composer (HMC). Dr. Harris was involved in the evaluation of early prototypes to guarantee compliance with his theory. User tests were undertaken to address usability problems. The HMC provides a graph editor with an intuitive graphical user interface for editing a Harris Matrix throughout the entire excavation process. It supports valid Harris Matrix creation and indicates invalid units and relations. The theory has been extended to allow for temporal relations as well. Furthermore units can be grouped into structural entities called phases and into periods, assigning them to a historical epoch. A powerful interface to the GIS system ArcGIS will be developed to access layers for visualization and analysis by selecting units of the Harris Matrix. In this way the HMC becomes also a unique tool for the management and retrieval of digital archaeological data.