Extension is the third album by composer/arranger/keyboardist Clare Fischer, and his first for big band, recorded and released in 1963 on the Pacific Jazz label, reissued on CD (together with the 1967 LP, Songs for Rainy Day Lovers) in 2002 as America the Beautiful,[4] and, under its original name, in 2012.

Reviewing the 2012 CD reissue for All About Jazz, Troy Collins calls Extension Fischer's "masterpiece," representing "a majestic culmination of his concepts, drawing upon myriad influences, including rich Ellingtonian voicings, the angular harmonic intervals of bebop, and bold modernist innovations proffered by classical composers such as Béla Bartók and Dmitri Shostakovich."

Expanding on this notion, Collins continues: Counter to the norms of the time, these meticulously scored big-band charts are light on extended improvisation—but intentionally so—as Fischer considered the relationship between composition and arrangement equally important.

Maintaining thematic control as primary soloist, Fischer proves to be a concise, yet original interpreter, demonstrated by his adroit pianism on the impressionistic tone poem "Quiet Dawn."

Together Fischer and Coker accentuate the date's prismatic colors and variegated moods, which are by turns charmingly old fashioned, like the breezy "Ornithardy," or subversively modern, such as the jaunty "Igor," dedicated to Stravinsky.