James Decker was Professor of Horn at the University of Southern California for 40 years. He also taught horn at the, University of California Long Beach, and was the horn instructor at the Music Academy of the West for more than 18 years. He was the horn teacher and chamber music instructor at the Bowdoin Summer Music Festival for 5 years and recently served on the faculty at the Kendall Betts Horn Camp. He was a member of  the board for the National Association of the Recording Arts and Sciences for talent scholarships and grants in classical music.

Most recently, James Decker was principal horn of the Los Angeles Chamber Orchestra for over 10 years. Previous experience includes principal horn of Kansas City, assistant principal horn of the National Symphony, guest principal horn of the Los Angeles Philharmonic, principal horn of the Columbia Orchestra, including the CBS recordings with Bruno Walter and Igor Stravinsky, and principal horn for over 2,000 major motion pictures and television series.

He was a founding member of the Los Angeles Horn Club, which commissioned over 100 new works for various horn ensembles, and was one of the founders of the International Horn Society, serving as host for two Workshops. He created the IVASI practice system, aiding young players in orchestral audition preparation with virtual conductors and entire horn parts. Finally, Jim has been a supporter and financial backer of Mark Veneklasen's revolutionary research into horn design and manufacture.