Kitab al-mustalhaq is an addendum to the treatises on Hebrew morphology by HayyuG, the most classic of the Andalusi works written during the caliphate of Cordoba and the benchmark for studies of the Hebrew language throughout the Arabic-speaking world during the medieval period. Kitab al-mustalhaq was composed in Zaragoza by Ibn Ganah after the civil war was unleashed in Cordoba in 1013. This new edition includes an historical introduction, taking account of the major contributions from the twentieth century to the present day, a description of the methodology and contents of this treatise, a description of the manuscripts, and a glossary of terminology. This new edition shows how Ibn Ganah updated his book until the end of his life.