Die Erarbeitung des DAGs begann unter der Leitung von Kurt Baldinger (1955-2006), der neben der Herausgabe des DAGs die parallele Erarbeitung eines Altokzitanischen Wörterbuchs vorsah (DAO/DAO Suppl). Im Jahr 2006 wurde das Projekt von Jean-Pierre Chambon neu konzipiert: Neu wurde im DAG_1300 (2006-2020) auf die parallele Redaktion des DAO verzichtet, da das Okzitanische mit dem Lexique roman ou dictionnaire de la langue des troubadours von Raynouard, dem Provenzalischen Supplement-Wörterbuch von Levy, dem Französischen etymologischen Wörterbuch von Wartburg und dem Dictionnaire de l’occitan médiéval (DOM) schon ungleich grössere Beachtung gefunden hatte. Zudem wurde die zeitliche Beschränkung auf die Anfänge der gaskognischen Scripta bis 1300 verkürzt und auf die Angabe der latinisierten und regionalfranzösischen Formen verzichtet. Seit 2014 läuft mit dem DAGél (Konzept und Leitung Martin Glessgen, unter Mitwirkung von Sabine Tittel) ein paralleles Projekt, dessen Ziel die Digitalisierung, Redaktion und elektronische Veröffentlichung des gesammelten lexikographischen Materials ist. Im Konzept des DAGél wurde der zeitliche Rahmen wieder bis 1500 erweitert und die Berücksichtigung der latinisierten altgaskognischen Formen sowie der delexikalischen Ortsnamen neuerlich eingeführt (cf. Glessgen/Tittel 2018 PDF).

To date, there is no dictionary that presents the vocabulary of the Old Gascon language separately or even in any satisfactory form. The only comprehensive lexicographical work is a 19th-century dictionary covering the Bearnese dialect and the Bayonne dialect (cf. Lespy/Raymond 1887), which is available in a 1997 edition that was slightly revised but not expanded.

Given the current state of research, it is difficult to determine whether Gascon should be considered a distinct language or a variety of Occitan. Although this question is not of decisive importance for the study of Gascon—the variety certainly deserves the full attention of linguistic history and geography (cf. Rohlfs 1970, 1)—it has occupied many researchers. The origins of this discussion date back as far as the Middle Ages, when Gascon was already understood as a distinct language, at least in contrast to the standard language of the troubadours: In the *Leys d’Amors*, a grammatical and poetological compendium from around 1350, the Occitan author classified it as a *lengatge estranh* (foreign language), listed alongside French, English, Spanish, and “Lombard.” Only a few linguists, such as Achille Luchaire (1879, 193), Kurt Baldinger (1962, 331f), or Georges Straka (1987, 408), have classified Gascon as a distinct language in more recent times, while many others, such as Mistral, Lespy, or Rohlfs (1966, 104 and 179), have highlighted its distinctive features, they tend to classify Gascon rather as a variety of Occitan (cf. Chambon/Greub 2002, 490; Field 2009, 751f). However, a clear classification of Gascon does not fully do justice to its complex situation: While (Proto)Gascon had already developed its characteristic phonetic features by 600 at the latest, Occitan was not yet recognizable at that time. An early 'splintering' of the Gascon variety, undoubtedly catalysed by its peripheral location and language contact, is therefore beyond doubt. Subsequently, Gascon continued to develop in close interaction with the neighboring Occitan varieties (cf. Chambon/Greub 2002, 492), which necessitated a mutual convergence.

For Kurt Baldinger (1919–2007), the research gap regarding the developmental history and historical characteristics of Gascon in southern Gallo-Romania served as the decisive starting point for this research project. The creation of the Old Gascon dictionary was intended to establish an entirely new foundation for understanding this previously neglected linguistic region of the Romance languages.

The DAG is a dictionary of the Old Gascon language as found in historical documents. It covers the vocabulary of the medieval stage of the Gascon language and its dialects (particularly Bordelais, Landais, Béarnais, Bigourdin, Comminges, and Val d'Aran). The source texts are of a legal and administrative nature: laws, notarial deeds, ordinances, administrative documents, court records, tax rolls, wills, feudal documents, and others.

The Gascon manuscripts are analyzed from the beginning of their written tradition in the 11th century through 1300 (Chambon project since ) or 1500 (directed by Baldinger 1955–2006 / DAGél, Glessgen since ). Chambon’s decision to limit DAG_1300 to the year 1300 and to exclude Latinized forms reduced the editorial material to about one-tenth of its original size. The time span under consideration was shortened to 150 years, beginning with the first purely Gascon texts in the mid-12th century, although it should be noted that a significant body of texts did not begin to appear until around 1230/40.

Earlier Gascon forms originate from Latin contexts. The chronological limit of the DAGél, which Glessgen extended to 1500, allows for the examination of lexical material spanning a period two centuries longer. The restriction to the year 1500 as the terminus ad quem is explained by the growing influence of French on Gascon, which had already been evident in its early stages since 12th century but intensified as a result of the Albigensian Crusade in the early 13th century and, above all, the Hundred Years’ War. With the incorporation of Gascony into the Crown lands in 1451/53, French began to supplant Gascon script, a process that was finalized in 1539 by the Ordonnance de Villers-Cotterêts. This ordinance established French as the sole language of administrative and legal texts, thereby replacing the Gascon scripts commonly used in these types of texts (cf.Baldinger 1962, 342).

An analysis of the language of legal documents provides a wealth of insights into the dynamic evolution of the vernacular, which becomes immediately apparent through the formulaic legal style. The subjects of the lawsuits and ordinances were people and their everyday problems, and so one finds everyday language at least as much in legal documents as in the language of fiction. A dictionary of legal language is, moreover, not only important for linguists but also indispensable for historians.