Most sociolinguistic investigations of variation and change in Arabic vernaculars focus on phonological features; a growing body of research deals with morphological/morpho-phonological features. This chapter synthesises research findings, focussing for the most part on variables common to several dialects spoken in a variety of communities. The findings provide evidence that the pattern of linguistic variation in many Arabic-speaking communities points to the emergence of new koinéised dialects which have assumed the role of local or regional standards in parts of the Arab world. In dialect contact zones, levelling of marked variants has led to the emergence of a range of variants. Social networks and frequency of contact appear to be the catalysts of linguistic change and the determinants of its direction.