The present article examines the integration of sophisticated harmonic and melodic techniques within the framework of popular song form in the music of Billy Strayhorn. Using the composition Isfahan, included in Ellington’s Far East Suite (1967), as a case study, we focus on compositional strategies and techniques which are recurrent in Strayhorn’s work. Subsequently, the use of these concepts is discussed in a comparative study with other Strayhorn staples, namely Chelsea Bridge and Passion Flower. The study shows how non-functional harmonic devices, including parallel harmony and constant structures along the minor third axis, as well as contrapuntal interplay between melody and bass line, are woven into the context of the functional harmony characteristic of the American Songbook, largely accounting for Strayhorn’s unique musical language. The paper also focuses on how these techniques coexist with other concepts extracted from the jazz idiom, such as blue notes and dominant chains, and how his more harmonically complex works actually have more in common with more standard Ellington/Strayhorn staples, such as Take the A Train or Don’t get around much anymore. In this sense, Strayhorn’s music remains firmly grounded in the tonal and structural conventions of mid-twentieth-century jazz, illustrating his capacity to expand the expressive possibilities of popular song forms without departing from their accessibility.