Karl Siegmund von Seckendorff (1745–1791) was a German composer and music theorist, primarily associated with the classical genre. He is best known for his contributions to the development of musical forms during the late 18th century, particularly in the realm of opera and chamber music. One of his notable works is the opera "Die Juden," which reflects his engagement with contemporary themes and the operatic style of his time. Seckendorff's compositions often showcased a blend of melodic invention and structural clarity, characteristic of the classical period. In addition to his compositional work, Seckendorff made significant contributions to music theory, particularly with his writings on harmony and musical aesthetics. His theoretical insights influenced contemporaries and helped shape the understanding of musical structure. While not as widely recognized as some of his contemporaries, Seckendorff's work laid groundwork for later developments in opera and classical music, making him an important figure in the transition from Baroque to Classical styles. His legacy is seen in the ongoing evolution of musical forms during the late 18th century.