This paper presents an analysis of the development and application of Charles Fillmore's case system (1968). The system is designed to determine semantic relationships (primarily of nouns) in linguistic deep structure. An historical overview of traditional grammar case labels and reviews of several other case systems are included. The appendix presents terms, definitions, and examples of several case systems for comparison. The strength of case theory is realized in the fact that there is not one "correct" or all inclusive case system. Rather, case theory is adaptable to a variety of conditions and analyses. Case roles are applicable to a variety of semantic structures and, therefore, case grammar theory proves valuable in areas from linguistic analysis to composition teaching. (Author/JK)