Peter, Paul & Mary was the most popular singing group in the U.S. before the Beatles arrived in 1964. Using three-part harmony arrangements, these gentle balladeers introduced the work of some of the best songwriters of the '60s. Formed in 1961 to capitalize on the folk music boom of the day, the group achieved huge success with their debut album, "Peter, Paul & Mary" (1962), reaching #1 on the charts and selling two million copies. The album, which included the hit singles "Lemon Tree" and "If I Had a Hammer" by the '50s-era folk group The Weavers, won Grammy Awards for Best Performance by a Vocal Group and Best Folk Recording. Sympathetic to the growing social and political movements of the era, the trio gave many performances at outdoor marches and rallies. The most significant of these found them with Bob Dylan at the August 1963 March on Washington, at which Dr. Martin Luther King, Jr., delivered his now-famous "I Have a Dream" speech.