A multitude of languages have used in the past, or use in the present scripts which are bidirectional. Phoenician, Aramaic, Old Hebrew (Canaanite), Jewish (Modern Hebrew, Yiddish, Ladino), Modern Arabic, Farsi, Urdu, Uigur, Kurdish are only a few to mention.

The total number of people currently speaking languages written in bidirectional scripts may be well above half a billion people, most of them located in the Middle East and Asia. Thus one can understand the ever increasing interest in the writing systems of these languages, their support in the computer environment, and the inclusion of their characters in the Unicode repertoire.

The peculiarities of the alphabets and of the bidirectional scripts are presented, along with the implications related to their data processing.

Remark for Unicode conference organizers: It is the intent of the author to develop this presentation in close cooperation and synchronization with another (distinct but presented immediately after) presentation on the typographic aspects of the alphabets with a Bidirectional script, to be given by Thomas Milo.