This study aims at identifying the concept of diglossia, its causes and methods of treatment, and its negative effects. The researchers used the descriptive method. The study revealed the following most important results: Firstly, the reason for language diglossia is contact between languages and emergence of new other languages or dialects which leads to a losing some of their original characteristics and qualities and the different environments within the same society that has a role in the emergence of diglossia. Secondly, it causes moving away from the mother tongue. Thirdly, the study also found that classical Arabic is the strongest ligament, which brings the peoples of the Arab nation together. Fourthly, diglossia can be reduced by simplifying classical rules of Arabic; facilitating the teaching methods and by paying attention to basic Arabic, which is supposed to be the focus of education for the emerging of mother tongue.