Since the seventeenth century, the Crónica Mexicayotl, an invaluable account documenting the Mexica Tenochca history, has been attributed either to Domingo de San Antón Muñón Chimalpahin Quauhtle-huanitzin, to Hernando de Alvarado Tezozomoc, or sometimes to both. To examine these attributions, we focus here on the way the document as we know it today was written, pointing out the fact that it was made by assembling material from several heterogeneous sources, among which we find the famous and now lost Crónica X. Important passages allow us to emphasize the role played by Tezozomoc in the composition of the original Crónica Mexicayotl, and to propose with reference to the later version that has reached us, that a considerable number of insertions can be attributed to Chimalpahin. In that regard we present two different hypotheses regarding the relationship of the Crónica Mexicayotl to other works, as well as to the authors Tezozomoc and Chimalpahin.