The App for Codex Mendoza represents the first effort in the world, to create a digital resource that allows a deep understanding of a Mexican codex. The National Institute of Anthropology and History (INAH) shows through this work, the propriety of this kind of editions and the necessity to find new forms of representation for such complex knowledge systems. This effort inscribes in INAHs permanent vocation for studying, preserving and communicating the vast cultural heritage of the Mexican peoples. Inside the application, the user may find all the folios from the three sections of the Codex, along with exterior and interior covers, added folios, signatures, seals, later handwritten inscriptions, and any detail that allows us the experience to digitally leaf through this foundational document for the Mexicans.The app includes functionalities such as: Transcription of manuscripts; the Hypermedia section, in which the user may find more about each folio, its pictograms and notes. In the Zoom section one may have access to details on the folios, otherwise imperceptible, getting us intimately close to this information. Inside the Maps and Calendars section, one may explore a Timeline of rulers territorial expansion, and about the tribute given by the governed towns, along with the taxing periods. The Codex Mendoza is the most relevant and iconic document, which describes the Empire ruled by the huey tlatoani Moctezuma Xocoyotzin, just after the arrival of the Spaniards. We could say that the studies around the Empires structure are only possible, thanks to the existence of this codex and its associated documents. The precise moment of the Codex Mendoza creation is open to debate, but a viable hypothesis places it between 1541 y 1542, indicating that it was Viceroy Mendoza who ordered its preparation.The processes of research, edition, design and production of this application, represents a huge effort of digital repatriation of this document now housed at the Bodleian Library in Oxford. The possibility to gain access through our tablets, to the richness, colour, and the valuable information provided by the Codex Mendoza is, with no doubt, good news for anyone interested in the history of Mexico.