Anne Sofie von Otter, a mezzo-soprano singer, performed at the Library of Congress with Thomas Dunford and Jonathan Cohen. (Ewa Marie Rundquist)

Anne Sofie von Otter has reached a career level at which she gets to do whatever the heck she wants. Historically, some classical singers — von Otter is a mezzo-soprano — have used this as an excuse to behave badly or indulge in sartorial excesses, but von Otter is using her power as wisely as she has pursued everything else in her career.

For one thing, she can work with whomever she wants. She is reacting to this by cherry-picking from the world’s store of massively gifted young artists to collaborate with on a variety of projects — including the lutenist Thomas Dunford and the keyboardist Jonathan Cohen, with whom she performed a (mostly) early-music concert at the Library of Congress on Tuesday night.

For another thing, she can do whatever she wants on stage. Nobody is going to tell her not to gesticulate, walk around or even play the tambourine. She does all of this tastefully, though, so the result is expressive, not excessive. Even her dress Tuesday reflected her performance: bright pink crushed velvet, cut in a simple silhouette evoking the Renaissance. It was at once strikingly vivid and supportive of the overall theme of the evening.

One of the marvelous things about Von Otter is that she can present an academic-sounding program without making it feel academic. Her contention is that John Dowland was an early singer-songwriter, and she certainly backed it up with her performance of “Can She Excuse My Wrongs” in which complex text and music became clear through her singing. In “Fine Knacks for Ladies,” the men joined in the singing (in harmony, thank you very much) as they played, while von Otter descended into a raucous chest voice, deliberately harsh.

It wasn’t the only delightful oddity on the program. The finale of the first half was a cantata by the Neapolitan composer Francesco Provenzale that juxtaposed high drama (the Queen of Sweden’s lament over her father’s death — von Otter called him her husband, but the program notes differed) with lusty folk songs and lullabies. Von Otter also offered the “shivering” aria of the Cold Genius from Purcell’s “King Arthur,” bringing every bit of chill to the music.

Von Otter sings with a natural expressivity and girlish beauty that are hard to match, but her collaborators, particularly Dunford, were worthy partners. Last month, Dunford played in another memorable trio recital at the Phillips, with harpsichord and Persian zarb, and there were a couple of echoes from that program, although his and Cohen’s rendition of Couperin’s “Les Barricades Mystérieuses” was considerably more restrained. Dunford is a fluid player who is able to follow von Otter, with the same effortlessness, from Charpentier to Kate Bush, who, along with Bjork, Sting, and Simon and Garfunkel, was represented on the program and sung with, if anything, even more delicate beauty (“Kathy’s Song” was meltingly gorgeous.)

The real measure of von Otter’s artistry may arguably have been Arvo Pärt’s “My Heart’s in the Highlands,” in which she basically sang the same words on the same sustained note, gradually moving up and down the scale but not changing the basic phrase, while the lute and harpsichord patterned around it. Making music out of a single note is a tall order for most singers. From von Otter, it was never less than riveting.