In the "Mouthpiece Series" of works for voice or voice and ensemble, the articulatory possibilities of the mouth are often mapped onto the instruments, mirroring and expanding the vocal sounds to form a kind of “super mouth” that can move beyond the physical limitations of a single vocal track. "There is a place here where there is a friction between what one expects to hear from a voice and what one actually hears in the music." Merging the voice with the breath and instruments has been the idea behind the Mouthpiece series, which began in 2000 and consists of more than 30 works for different sound combinations, devoid of semantic text or language. 

In 2022, Erin Gee was awarded the Arts and Letters Awards in Music from the American Academy of Arts and Letters. Her debut portrait CD, "Mouthpieces" is on the col legno label in Vienna. Other works can be found on CDs by the TAK ensemble, Ekmeles Ensemble and the International Contemporary Ensemble.

Gee’s awards for composition include a Guggenheim Fellowship, Zürich Opera House’s Teatro Minimo, a Radcliffe Fellowship, the Rostrum of Composers Award, Koussevitzy Award, Fromm Commission, the 2008 Rome Prize, among others. She has been commissioned by the Zurich Opera House for the opera SLEEP, by the Radio Symphony Orchestra Vienna, the Los Angeles Philharmonic New Music Group under Esa-Pekka Salonen, by Klangforum Wien, Dal Niente and others.