Beach, who is currently director of Purchase College's Performing Arts Center, succeeds Mary Lou Aleskie, who left LJMS in September to join the International Festival of Arts and Ideas in New Haven.
At Purchase College, part of the State University of New York, Beach oversaw the design of the center's $3.2 million renovation, and under his 16-year tenure the center's budget grew from $1.2 million to $5.2 million.
"La Jolla Music Society's impressive commitment to artistic excellence and community involvement is well-recognized throughout the country," Beach said in a statement. "It is a privilege to be entrusted with this distinguished 37-year-old institution, which is the major presenter of classical music in San Diego County and a leading performing arts presenter [on the West Coast]."
LJMS's 3005-06 season began on October 5 with a performance by violinist Nicola Benedetti. Season highlights include the West Coast premiere of Osvaldo Golijov's Ayre.