Abstract The so-called Mediterranean Lingua Franca is a Romance-based, only-spoken linguistic variety that in slavery and travel accounts of the 17 th –18 th centuries is said to have been used by Moors and Turks, mainly in North Africa and above all in Algiers, as a basic means of communication with Christian slaves. Its only lexicographic source is an anonymous dictionary printed in Marseille in 1830, which is devoted to the Lingua Franca as it was spoken in Algiers. This source is by far the richest one available, but also the most problematic, because of its many inconsistencies and contradictions. As a result, the lexical components of the Algerian Lingua Franca (mainly Italian and Spanish, but also French, Provençal, Arabic, Turkish, etc.) as well as the quantity and quality of their contributions can only be reconstructed by critically comparing the entries of the Dictionnaire of 1830 with all preceding records by former prisoners and travellers.