This chapter discusses the concept of ‘traditional dialect’ in the light of Arabic data. The term is often used impressionistically with little or no attempt to narrow down its meaning in terms of specific attributes. The paper also tries to discuss this notion beyond a social perimeter and see how it can be characterised linguistically, both in synchrony and diachrony. Synchronically, it suggests that traditional dialects have to exhibit a sufficient number of features that distinguish them from the standard or target varieties. Diachronically, it puts forward the idea that traditional dialects should display a relative linguistic stability over time.