Bluegrass is one of the most rigid music genres, one that steadfastly refuses to change its direction. Therefore, Progressive Bluegrass is viewed with skepticism at best, derision at worst, by some hardcore bluegrass fans. Progressive bluegrass expands the sonic palette of bluegrass either by adding elements of jazz, folk, country, and rock, or by amplifying the instruments. The subgenre developed in the late '60s, but it flourished in the '70s, when bands like the Dillards, Boone Creek, Country Gazette, and New Grass Revival began coming to the forefront of bluegrass and folk festivals. Throughout the '80s and '90s, progressive bluegrass continued to evolve, moving closer toward folk and rock in some quarters and closer to jazz in others.