Rabbi Jonah ibn Genach (Hebrew: יונה אבן ג'נאח, Arabic: أبو الوليد مروان إبن جناح Abu-l-walīd Marwān ibn Janāh, Latin: Marinus) (ca. 990 in Córdoba - ca. 1050 in Saragossa), was the most important Hebrew grammarian and lexicographer of the Middle Ages. He was born in Córdoba, and studied in Lucena after leaving his native city in 1012. After wandering Iberia, he finally settled in Saragossa. Rabbi Jonah was known to his contemporaries by his Arabic name Abu-l-walid, while the name ibn Janah (Arabic: "winged") may have been appended because of his Hebrew name Yonah (Hebrew: "dove"‎).
He had training as a physician and is mentioned elsewhere as the author of a medical text, but seems to have found his true calling in the investigation of the Hebrew language and in scriptural exegesis. Although he wrote no actual commentary on the Hebrew Bible, his philological works exercised the greatest influence on Judaic exegesis and form the basis of many modern interpretations.
Rabbi Jonah's first work, al-Mustalha ("Complement"), is a critique and expansion of the work of David Hayyuj, the founder of systematic Hebrew grammar studies. He is best known for the Kitab al-tanqih ("Book of Exact Investigation"), which is divided into two parts: the Kitab al-luma ("Book of the Many-Coloured Flower Beds") and the Kitab al-usul ("Book of the Roots"). The first focuses on the grammar of Hebrew, the second its lexicon. Rabbi Jonah's last work, his Kitab al-Tashwir ("Book of Refutation"), is largely lost. Like most Spanish Jews of the time, his works were written in Arabic.