This thesis is a study of four compositions written by Fanny Mendelssohn Hensel, older sister of Felix Mendelssohn. Her music is compared with four pieces composed by Felix. This study shows that Fanny was a gifted and creative composer, even surpassing Felix and predating Brahms with her compositional ideas and progressive uses of harmony. Despite her excellent education and recognition among those who knew her well, she did not publicize her talent in any way because of pressure from her father, Abraham, and Felix to stay within the prescribed societal confines of wife and mother.