John Arden "Jay" Ferguson (born May 10, 1947) is an American rock and pop musician known for his work with the bands Spirit and Jo Jo Gunne, and his 1978 solo hit "Thunder Island". His later career has been as a composer of music for television programs and films. Many people know Ferguson for composing the theme song for the American version of The Office on NBC.

Ferguson was born on May 10, 1947, in Burbank in the San Fernando Valley, California, to John Becker and Kathleen Jane Ferguson. He grew up in the Van Nuys and Canoga Park sections of Los Angeles. Along with his brother Tom, an accomplished fiddle player, he formed a bluegrass group called The Oat Hill Stump Straddlers including Michael Fondiler and Steve Fondiler. He also held part-time jobs at different points as a theater usher and an architect's assistant for his father John Ferguson, taught piano in a music store, and studied at UCLA after high school.

Spirit was founded in the mid-1960s. Many musicians of the time cited The Beatles and their music as an influence, and Ferguson was no exception. Reuniting with longtime musician friends Randy California and California's stepfather Ed Cassidy, who, with Mark Andes and John Locke were in a band called the Red Roosters - Ferguson joined with them to form a jazz-influenced rock group that was originally called Spirits Rebellious, after a Khalil Gibran passage. They later shortened the name to Spirit. Ferguson was the last member to join the band. Ferguson shared singing and songwriting duties with California, writing most of the songs on their first album. Spirit began playing at various nightclubs and concerts in the Los Angeles area, especially the clubs along the Sunset Strip, including Whisky a Go Go. At one of these shows, French film producer Jacques Demy saw Spirit perform and decided he wanted them in his next film. It led to a cameo role for the band and a short speaking part in which Ferguson played a character based loosely on himself in the film Model Shop. Spirit also provided much of the instrumental soundtrack. In 1982, after his sixth and last solo album, White Noise, Ferguson decided to become a soundtrack composer for movies and television. He has written music for over 15 feature films and many TV shows. His most recognizable composition as a TV and film scorer is the theme to the NBC-TV version of The Office, which won him the 2007 Film & TV Music Award for Best Score for a Comedy Television Program. (In The Office, he is also the guitarist in Kevin's band "Scrantonicity".) He is the composer of "Pictures of You" from the soundtrack to The Terminator, and the entire score to A Nightmare on Elm Street 5: The Dream Child, Bad Dreams, the Tales From The Crypt episode "Forever Ambergris", as well as Tremors 2: Aftershocks, and Tremors 4: The Legend Begins. Ferguson is also the current soundtrack composer for NCIS: Los Angeles, having replaced original composer James S. Levine halfway through season one with Ferguson's music debuting in the season 1 episode, "Chinatown".