No concert, however epic in duration, could encompass the entirety of the contemporary classical world, which has grown too broad and variegated to sample in one sitting. But as a microcosm of the teeming activity that falls under the broad umbrella of the new-music rubric, the Music of Now Marathon, a recently instituted annual event at Symphony Space, does nicely. Programmed by Laura Kaminsky, a composer and Symphony Space’s artistic director, the marathon is the opening event in Composers Now, a monthlong series organized by Tania León, which includes dozens of concerts throughout the city.

 Just what criteria were used to select and order the composers and artists who appeared in Music of Now, held on Saturday afternoon and evening, went unrevealed. What was offered was a friendly succession of interviews, in which Ms. Kaminsky and Ms. León asked composers about their methods and motivations, followed by performances: Query, play, repeat.

If the marathon made no sweeping statements about the general trajectory of modern music, the opening work, Libby Larsen’s 1991 string quartet, “Schoenberg, Schenker, Schillinger,” offered one pertinent view. Its three movements evoke three foundational concepts of 20th-century music: Arnold Schoenberg’s revolutionary 12-tone technique; Heinrich Schenker’s essentialist approach to harmonic analysis; and Joseph Schillinger’s math-based methodology.

The sequence, Ms. Larsen explained onstage, illustrates her belief that a shift in focus from melody toward rhythm has been central to the way music is perceived now. Played by the Cassatt Quartet, the coolly meandering “Schoenberg” movement had an ineffable melancholy; the concluding “Schillinger” section, a cheery vitality.

Heedless of manifestoes, the concert wound through straightforward melodicism and rhythmic buoyancy in Octavio Vazquez’s Trio for Oboe, Bassoon and Piano, given its premiere by the Poulenc Trio; a subtle weaving of individual and collective strands in Anna Weesner’s work “The Space Between,” played by the Cassatt Quartet; a haunting distillation of drama without words in Susan Botti’s “Gates of Silence,” performed by Ensemble Pi; and Errollyn Wallen’s playfully eclectic, pop-savvy songs and piano works, which she presented with exuberance and wit.

The most striking part of the five-hour stretch I attended came during a segment featuring Angélica Negrón, a gifted young composer born in Puerto Rico and living in Brooklyn. She offered two dreamy pieces, “Cosmovisión” and “El Reloj,” with a trio that combined her voice, accordion and musical toys with Nuiko Wadden’s harp and Shayna Dunkelman’s xylosynth, a sampling keyboard played with mallets.

Ms. Negrón, born in 1981, comes from a generation of composers for whom engagement with pop music extends past familiarity to hands-on facility — she also plays and sings in an electro-pop band, Balún. The two wistful confections she presented here would have been equally at home in a downtown nightclub or a Brooklyn loft space.