"Mysticism," according to the Oxford dictionary, can be defined as "belief in or devotion to the spiritual apprehension of truths inaccessible to the intellect." More generally, it applies to the aspects of spirituality and religion that can only be directly experienced, rather than described or learned. This dissertation examines how mysticism fits into the aesthetic, compositional, and musical philosophies of four prominent composers of the 20th and 21st centuries—Ernest Bloch, Olivier Messiaen, Sophia Gubaidulina, and John Zorn, with a cameo by the Jewish composer David Finko—and how their engagement with the concept of mysticism and the mystical experience can be seen in a selection of their works featuring the violin: Bloch's Baal Shem suite and Poème mystique; Finko's Lamentations of Jeremiah, Zorn's Kol Nidre, Goetia, All Hallow's Eve, and Amour fou; Gubaidulina's In tempus praesens; and Messiaen's Quartet for the End of Time. These works exemplify the mysticism shared by these composers, despite their different religious and cultural backgrounds, particularly their belief in the transcendental nature of music. This belief is expressed in their works through programmatic, melodic, harmonic, rhythmic, and formal elements, all of which display, to a greater or lesser degree, the influence of mystical philosophy and symbolism.