The Hollywood Chamber Orchestra (HCO) is an American orchestra based in Los Angeles, California, and founded in 2015 by musicians Noah Gladstone and Mark Robertson, who are also co-music directors. Its first public performance was on August 8, 2015, at the Colburn School's Zipper Hall. The program consisted of all horn concertos and was presented by the 2015 International Horn Society. Included on the program was the world premiere of Brad Warnaar's horn concerto, conducted by the composer and performed by Andrew Bain, the principal horn player of the Los Angeles Philharmonic. Their first public ticketed concert occurred on December 11, 2015, at the Montalban Theatre in Hollywood, featuring Vivaldi's Four Seasons, performed by Los Angeles Philharmonic concertmaster Martin Chalifour. Subseq