The case category is a grammatical category that exists in most of the world's languages, but it is not a single system for all languages, it is a grammatical category that appears with its own characteristics due to the laws of development of each language. Although there are several types of case in world languages, for Turkish languages there is one type is characteristic.In the Orkhon-Yenisei monuments, there were nine cases of the noun, the ninth case was called the instrumental-joint case. The same situation can also be found in Uighur written monuments. In modern times, the joint case in the Kazakh, Karachay-Balkar, Karaim, Khakas, Shor, Chuvash, and Yakut languages existed as the seventh case in the grammar books of the Azerbaijani language until 1939, but later it was removed from the textbooks and only six cases were preserved.Methods: Since the case category exists historically in world languages, including Turkish and Azerbaijani languages, diachronic, synchronic, as well as comparative-historical and comparative-typological methods were used in the article.