According to program notes by Jack Gottlieb, one of Bernstein's assistants, the story of the piece may be summarized as follows: {{Ordered list|type=upper-roman
Prologue The music begins in emphatic fashion: a
pickup G, which is then followed by a C that jumps up to an F (a
tritone). A chromatic 3-note sequence follows. The low instruments then begin playing a theme that would perpetuate the rest of the piece. The music evolves into a dance, played by the violins and the woodwinds. The dance is interrupted several times, until it finally climaxes in a way that resembles the opening bars of the piece. The new section is characterized by sudden jumps by higher instruments, accompanied by a 7-note
syncopated baseline. Multiple denser parts and different melodies dot the section, until a whistle sounds. A quieter section follows concluding the Prologue.
Somewhere The music follows into "
Somewhere", a slow Adagio which is first played by solo strings. A romantic horn melody follows soon after, which resolves into a high cry by the upper strings, with the cellos and low woodwinds playing descending passages. An intermezzo follows, containing remnants of the previous melody. The original horn melody is then passed onto the seconds and violas, accompanied by the firsts, piano, and harp. A denser cry is then played, which resolves. The flute then plays a quiet melody, and the violins and trumpets lead into a faster section. The faster section is characterized by remnants of the previous slower section. It accelerates, until it reaches the Scherzo section.
Scherzo The
Scherzo is made up of a playful melody by the woodwinds and violins, often dotted by other instruments with their own small section. It seemingly repeats multiple times, but the section concludes with a recap, and a final uttering of the cry in "Somewhere".
Mambo Mambo is a much faster-paced section. The section features percussion playing many complex rhythmic lines, upper strings and low woodwinds playing a dancing melody, and an offbeat rhythm by the bass drum and double bass. Brass sections dot this section, and tension is built until a crucial 4-bar passage is played: a unified section of notes, and the orchestra yelling “Mambo!” An intermezzo is played, and “Mambo!” is repeated. A trumpet rhythm rhythm follows, with complex accompaniment from the rest of the orchestra. Interruptions coming from the rest of the orchestra dot the section, until an earlier part of "Mambo" is restated. The section dies down and slows to transition into the next section.
Cha-cha The Cha-cha is characterized by a quiet mainline melody, with a waltz-like accompaniment. It is traced back to the
Cha-cha-cha, a dance of Cuban origin. The bass clarinet starts off with the melody, with hints of violin
pizzicato and high woodwinds dotting the section. A procession played by the violins then follows. Suddenly, an
arpeggio by the
celesta follows into the next section.
Meeting Scene "Meeting Scene" is derived from “
Maria” from the original
West Side Story. A high pitched solo violin melody, in which the other strings sometimes join in. The basses start a long A, which crescendos into the next section.
Cool "
Cool" is a section in which a jazzy
fugue is repeated by different instruments. It first starts very low, building steadily as higher instruments join, until a percussive E–A–E breaks in. The flutes then take over the melody, which is sometimes interrupted by other melodies. Other instruments join in the melody, until a trumpet takes over, by playing repeated crescendo passages which pop at the end of the phrase. A new fugue is then played, starting with the flutes, then the clarinets, then the entire woodwind section. A
swung section is then played by the woodwinds and low strings, dotted by percussive hits from other instruments. More jazzy rhythmic melodies follow, until the next section suddenly slows.
Rumble "Rumble" suddenly interrupts "Cool", with percussive hits dotting the piece. A fight is played as a main melody, which is accompanied by a rhythmic bassline. More percussive hits follow. Scurrying from syncopated instruments dot the piece, which then ascends into a high popping
tremolo. A chromatic 3-note series follows, which is succeeded by a flute
cadenza.
Finale "Finale" echoes the second section of "Somewhere", as a high romantic melody is played by the upper strings. Basic accompaniment comes from the lower strings. A shrill cry is played as the final closing notes of the violin melody. Oboes and trumpets take over from the violins, with steady pizzicatos coming from the lower strings. Upper strings and upper woodwinds play closing notes to the section, and a final cadence concludes the piece. ==Recordings==