Colorado MahlerFest is an annual event held in Boulder, Colorado, which each year celebrates one major symphonic work by Austrian composer Gustav Mahler. While "Colorado MahlerFest" is the official name of the event and the organization, the individual annual events are simply referred to as "MahlerFest" (dropping the "Colorado"), followed by a Roman numeral.
MahlerFest was originally held every year during the second week of January, on the University of Colorado at Boulder campus, and in 2009 was switched to the middle of May (the University leases its facilities during the academic break). Volunteer orchestral musicians donate their services for two performances of one major work by Mahler on Saturday night and Sunday afternoon (typically the weekend of Martin Luther King, Jr. Day); a symposium is held on the Saturday of the festival, in which Mahler scholars discuss aspects of that year's work; and a series of "Visualizing Mahler" art exhibits, which feature artists reactions to that year's Mahler composition, are held in various places throughout Boulder.
The founder of MahlerFest was conductor Robert Olson, who currently serves on the faculty of the University of Missouri–Kansas City who led the festival until his retirement in 2015. Kenneth Woods succeed Olson as Artistic Director in 2016.
Colorado MahlerFest received the gold medal of the International Gustav Mahler Society in Vienna in September 2005.