Joseph Guillaume François "Jef" Denyn (19 March 1862 – 2 October 1941) was a pioneering Belgian carillon player and composer from Mechelen. Initially pursuing engineering, Denyn's career in carilloning began in 1881 when he took over from his father, Adolf Denyn, the official carilloneer of Mechelen, after his father became blind. Officially appointed to the position in 1887, Jef Denyn was instrumental in reviving the art of the carillon, which had declined in the 19th century due to wars and societal changes.

Denyn's engineering background enabled him to innovate carillon technology significantly, leading to improvements that became standard across Europe and the United States. He introduced a new connecting system that enhanced the instrument's playability, allowing for more expressive performances. His virtuosity and technical innovations helped re-establish the carillon as a respected musical instrument.

In 1922, Denyn founded the Royal Carillon School "Jef Denyn" in Mechelen, the first international institute dedicated to the study of campanology, which remains a leading institution in the field. During World War I, Denyn and his family sought refuge in England, where they were hosted by organist William Wooding Starmer in Tunbridge Wells.

Denyn's contributions to carillon music, both as a performer and an innovator, have left a lasting legacy, and his techniques and improvements continue to influence carillon construction and performance today.