As is the case with Marie de France herself, very little is known about her collection of lays, including for whom or why they were written, and whether they were even intended to be presented as a unified collection. The date of composition has been placed between 1160 and 1199, though for a long time it was believed that they were written as late as the 13th century (a belief no longer substantiated by the evidence). This was a period of cultural renaissance in the midst of the Early Middle Ages (the period commonly called 'the dark ages'), and Marie is one of several authors from that century whose work continues to resonate. What was unique at the time was the use of vernacular (French or English, the spoken languages of the two cultures that thrived in this renaissance), rather than the traditional Latin. For the first time, the use of vernacular was not immediately considered inferior to Latin, and her use of French suggests that the purpose of the work fit within a larger entertainment context than had existed before.
The narrative lay was a somewhat new form, amongst the more popular romances and chanson de gestes. Marie is one of the earliest writers who wrote narrative lays--essentially short narrative poems--whereas the more traditional lays were based on a much older form that was used primarily to immortalize heroes or carry on folk tales, and was traditionally performed alongside music. However, there is much reason to believe that Marie did not intend these lays to be performed to music, but rather to be read or perhaps narrated. Marie wrote the lays in French octosyllabic couplets, and they range from about 115 to 1180 lines.
Whether or not Marie intended these works to be presented as a single collection, it is worth studying them as a unified whole because of the depth Marie's vision takes when one notices the parallels that emerge between the stories. She drew upon an eclectic wellspring of influences ranging from Celtic folklore to classical myths and stories to legends popular in her contemporary chivalrous culture (such as King Arthur). However, she adapts them all to a Briton setting very immersed in the courts of chivalry, suggesting that she wanted to please her particular audience.
Overall, the lays present a subversive examination of the popular values of chivalry (particularly the selfishness and self-glorification contained in them) while at the same time celebrating that same culture. Characters tend to lack psychological personality even when Marie uses omniscient perspective, although they are ultimately defined and judged by the actions they take. While the lays are primarily concerned with love, Marie uses these romantic situations to probe various questions of, for example, obligation, fate, and class, through them, with a willingness to present different values for different situations, ultimately revealing a profound understand of the innate human tendency towards contradiction and complexity.