The thesis explores the relationship between text and music in vocal composition through examinations of Olivier Messiaen´s song cycle Harawi, the first part of a trilogy based on the medieval Tristan story. Messiaen wrote his own lyrics for the composition, as he did for nearly all of his vocal works, arguing that his music were too complex to combine with a pre-existent poem. Strongly influenced by Surrealism, his textual line balances between a semantically meaningful and a purely onomatopoeic expression. Accordingly, the study examines the interaction between the sonority of the text and the musical line, as well as how the musico-poetic material correlates with Messiaen´s reading of the Tristan myth. The thesis´ analysis (chapter 5) is divided into three parts. The first part examines the coherence of the composition, as Messiaen makes considerable use of structuring material both in text and music. The second part considers the surrealistic influence on the songs, particularly how the music reflects the surrealistic imagery of the text. The final part treats the text´s phonetic aspects, by looking at Messiaen´s employment of onomatopoeic material, derived from the Peruvian dialect Quechua. Besides, the study aims at placing the composition within an aesthetic, historical and theoretical context, always with the question of text-music relationship in mind.