The only Old Breton extant words are glosses in Latin manuscripts from the 9th and 10th centuries, now scattered in libraries and collections throughout Europe. It is likely there was a highly developed oral tradition during the Old Breton period. And on the evidence of Breton names, it would appear that Old Breton literature inspired much of Arthurian literature, the story of Tristan and Iseult and the romances of Chrétien de Troyes.
The earliest known piece of extant Breton literature is found in the margins of a 14th century Latin manuscript, scribbled by a scribe weary of his toil and mind on more immediate concerns, he left for posterity a four line love poem, the first two lines beginning:
The main principle of Breton poetry, complex to achieve, is that the next to last syllable in a line should rhyme with one or more other syllables in the same line. For example in the first line above, "en" is the second to last syllable, which rhymes with "guen" and "heguen". In the second line, "at" is the second to last syllable which rhymes with "hegarat".
There are several texts from the 15th century:
In the 1920s a movement, in which the linguist and author Roparz Hemon played an important part, arose to introduce the trends of modern literature into Breton. The literary magazine Gwalarn provided an outlet for modern authors, such as Jakez Riou and Yves Le Drézen (who published the first long novel in Breton in 1941).
Pierre-Jakez Hélias (1914-1995) wrote prose and poetry in both Breton and French. His contemporary Añjela Duval (1905-1981) wrote poetry reflective of her peasant origins, mysticism, and social conscience.