Although the significance of her achievements has not yet been widely recognized by the musical establishment, the music and aesthetic philosophies of Lucia Dlugoszewski (1931-2000) distinguish her as one of the most original and creative American composers of the twentieth century. Drawing comparisons to Henry Cowell, John Cage, Harry Partch, and her teacher - Edgard Varèse, her music encapsulates the philosophies and developments for which these composers are best known. Her invention of the "timbre piano" in 1951 advanced with greater sophistication the sonic expansions of the piano that were first explored by Cowell and Cage; this and her invention of an orchestra of one hundred new percussion instruments allowed the creation of a highly idiosyncratic music structured primarily on timbral and dynamic contrasts. Collaborating throughout her career with noted choreographer Erick Hawkins, Dlugoszewski sought to create a new mode of artistic expression that was heavily based on the concepts of sensual realism, "Suchness" and "Otherness" (as found in Zen Buddhism and haiku poetry), and other abstract philosophical doctrines in the pursuit of the dialectic compatibility of sound, movement, and theatre; further collaborations with film makers, painters, poets, and the notoriously provocative dramatic company, The Living Theatre, established a deep and profound influence on the whole of the New York avant-garde. Despite her imaginative and unique contributions to experimental music, Dlugoszewski's professional choices, gender, and her rejection of contemporary trends in modern music (e.g. serial methods, chance operations) largely sheltered her from the attention of the mainstream musical community, and this research represents the first substantial scholarship on her life and music. With a thorough review of available information and the cooperation of performers who knew her as a colleague and friend, this document will provide a complete biographical history, an exploration of her philosophical and aesthetic principles, and the first detailed examination of her invented percussion instruments.