This year's Mostly Mozart Festival holds a few surprises for New York City audiences — for one thing, Mozart will assume a smaller role at his own festival. Of course, works by Mozart and his contemporaries are part of the offerings, including his Requiem and "Linz" Symphony, and an opening-week focus on Beethoven. But organizers are also evoking Mozart's joy in discovering new sounds and in encountering the unexpected.

Part of that exploration is the establishment of Mostly Mozart's first-ever composer-in-residence: 46-year-old Argentine composer Osvaldo Golijov.

In just a few short years, Golijov, who won two Grammy Awards this winter for his opera Ainadamar, has emerged as one of today's most popular new voices. At once not easily categorized, superbly layered, and sensitively nuanced, his compositions have been rapturously embraced by performers, critics, and audiences alike.

Mostly Mozart is lavishly celebrating Golijov's work. First up is the New York premiere of his cello concerto, Azul, on July 31 (repeated on August 1). Later come two performances of his groundbreaking Pasión según San Marcos (The Passion According to St. Mark) on August 18 and 19, with a special late-night Latin jam session following the Passion's performance on the 19th. On August 20 and 23, Mostly Mozart presents a concert exploring works by Monteverdi and Schubert, two composers who have greatly inspired Golijov.

In addition to Golijov's influence on the Festival, other highlights this summer include four encore performances of Mark Morris's acclaimed "Mozart Dances," commissioned last year; the opening week Beethoven focus that culminates in a four-hour marathon featuring the Swedish Radio Choir and Mostly Mozart Festival Orchestra under Music Director Louis Langrée; and an over-arching spiritual theme featuring Breath, a new art installation by the OpenEnded Group on Avery Fisher Hall's façade, as well as choral works from the past five centuries, including Golijov's Pasión.

Jane Moss, Artistic Director of Mostly Mozart, says that adding a composer-in-residence to the festival's programming is part of Mostly Mozart's evolution. "It's part of some larger changes that have taken place over the last ten years," she explains, "in which we've also added period-instrument performances, opera productions, late-night concerts, and newly commissioned works to the mix. Last year, for example, for the 250th anniversary of Mozart's birth, we commissioned a violin concerto by the Finnish composer Magnus Lindberg."

As Moss proudly remarks, "We really have the beginning of a happening festival at Mostly Mozart." She adds that the evolution in Mostly Mozart programming is "really connecting with an audience — and new audiences at that."

But why add new music per se to a New York summertime institution? "We love the idea of having a composer as a living presence at the festival," Moss says, "not just to create new works related to Mozart, but also to add a curatorial voice in terms of the classical and baroque music we present during Mostly Mozart."

In his role as a co-curator, Golijov suggested the concerts of Monteverdi and Schubert. Monteverdi's Vespers of 1610 (also known as the Vespro della Beata Vergine) will be performed on August 20 by the period-instrument ensemble I Barocchisti and the Swiss Radio Chorus of Lugano — both making their U.S. debuts. On August 23, conductor Frans Brüggen and the Orchestra of the 18th Century will play Schubert's Symphony No. 8 in B minor, D. 759 ("Unfinished") and the Symphony No. 9 in C Major, D. 944 ("Great").

"The Monteverdi Vespers is my favorite piece," Golijov reveals. "Also, including it gives the programming such a nice arch. The Monteverdi is this big piece from 1610; then, on August 24 and 25, we have the Schola Cantorum de Caracas singing the Mozart Requiem from 1791, nearly 200 years after the Monteverdi; and then my Passion written about 200 years, give or take a few, after the Mozart. Of course," he says with a laugh, "my contribution is by far the smallest bit! But it's a presentation with great chronological symmetry."

Golijov says that Monteverdi was incredibly forward thinking in his writing. "The Vespers show such tremendous originality of thought, of sound," the contemporary composer muses. "Bar by bar, it sounds not like it was written nearly 400 years ago, but instead as if it was written this morning. His ideas of tempos, harmony, rhythmic relationships — all of those elements that Monteverdi sets out in the Vespers were left aside for the next 300 years compositionally."

In terms of programming the two Schubert symphonies, Golijov says, "My sentiments were only personal and very selfish — I love them so much!" he says. The composer adores Schubert's expansive spirit. "Instead of writing a very directional music that goes directly from Point A to Point B to Point C," he notes, "Schubert allows for detours, for getting lost in the forest a little bit, stopping to have some water, looking at the birds, falling asleep — it's a really different way of narrating."

Another of Golijov's own compositions at Mostly Mozart will be his cello concerto, Azul, which Moss jokes will be enjoying its "indoor premiere"; it was commissioned by the Boston Symphony Orchestra and premiered at the BSO's summer home, Tanglewood, last August. The Boston Globe termed Azul "music that has instant appeal, [with] a glowing surface of sound."

Golijov says that the New York premiere of Azul (with soloist Alisa Weilerstein, the Mostly Mozart Festival Orchestra, and Louis Langrée) offers a chance to tinker with the work. "I didn't like the cello concerto when it premiered, so I'm revising it!" he notes with his characteristic blend of humility and good humor.

After roaringly successful, sold-out presentations of the Passion at the Brooklyn Academy of Music in 2002 and as part of Great Performers' "The Passion of Osvaldo Golijov" festival at Lincoln Center last spring, that kaleidoscopic work returns during Mostly Mozart with conductor Robert Spano leading a vast array of forces, including the celebrated Brazilian vocalist Luciana Souza, soprano Jessica Rivera, capoiera and berimbau player Deraldo Ferrira, vocalist and dancer Reynaldo González Fernández, and the Orquesta La Pasión, along with a Venezuelan chorus, the Schola Cantorum de Caracas, directed by Maria Guinand.

In Passion, Golijov — a Jewish composer — takes one of Christianity's urtexts and weaves together shifting narrative identities, Bahían drums, Afro-Cuban dance rhythms, the Jewish mourning prayer of Kaddish, and African-influenced call-and-response singing into a mesmerizing and awe-inspiring event.

Golijov is thrilled that the Venezuelan choir will be heard by New York audiences performing not just his Passion, but other repertoire as well; on August 24 and 25, they will present a program of contemporary a cappella choral works from South America, in a pairing with Mozart's Requiem. "It's absolutely great that they are doing this other performance," he declares. "Although my Passion has become a signature work for them, they're incredibly special in traditional repertoire."

Those surprising programmatic juxtapositions, according to Golijov, are precisely what he intends for Mostly Mozart. "Sometimes," he reflects, "it's important to see where the spirit of Mozart leads us, rather than just programming his music. It's like what Peter Sellars [the famed director and frequent Golijov collaborator] did when he was invited to Vienna to curate a festival for Mozart's 250th. Peter didn't program a single Mozart work — instead, it was all new music," the composer notes. "I think that we should be asking ourselves, 'What was Mozart saying? What was being said before him, and what was said after him?' If Mozart were alive today, I truly believe that he'd be programming this way."

Anastasia Tsioulcas writes frequently about the arts.