In the Middle Ages, Jews in Arab lands used both Judaeo-Arabic and Hebrew as their literary languages. Mediaeval Judaeo-Arabic texts are written in Middle Arabic, which contains classical and later elements. The latter do not appear in standard dictionaries of Classical Arabic, and it is to these post-classical, neo-Arabic, and pseudo-correct terms and expressions, which to a great extent are identical with Middle Arabic elements found in other Arabic writings of the period, that Joshua Blau's Dictionary of Mediaeval Judaeo-Arabic Texts is primarily devoted. The Dictionary is based largely on the works of the leading Jewish scholars of the period, including Saadia Gaon, Judah Halevi, and Maimonides, but it also refers to the Responsa literature, legal documents, and personal and commercial letters. This first comprehensive dictionary of Mediaeval Judaeo-Arabic contains about 9,000 entries. The lemmas are presented in both Arabic and Hebrew scripts, and are translated into Hebrew and English. A special section is devoted to lexicographical literature.