Beethoven is generally acknowledged to be the most important composer of the 19th century. However, many critics and musicologists dismiss Beethoven's Lieder as being of less musical value and sophistication than his more instrumentally conceived late vocal writings. The true musical sophistication of Beethoven's Lieder can be discovered by a careful study of the harmonic structure and the relationship between the vocal and the piano part in Beethoven's Lieder. In discussing Beethoven's Lieder style based on analysis, a number of aspects shall be examined: (1) the harmonic idiom and key relationships; (2) the role of the piano; and (3) other stylistic features.