This paper analyses borrowings of possible Illyrian provenance in Slavic. Sections 1 and 2 describe previous attempts at defining the borders and characteristics of the Illyrian language. The Illyrian forms are classified according to the system of anthroponymic areas of Illyricum established by Radoslav Katičić. Thus, they are labelled as either Liburnian, Delmato-Pannonian, or Illyrian proper. The main part of the material, covered in sections 3 and 4, consists of 59 onomastic and lexical items generally held to be Illyrian borrowings into Serbo-Croatian and, to a lesser extent, into Bulgarian and Slovene, often with cognates in Albanian and Romanian. The Illyrian origin of 13 forms is rejected. Section 5 discusses another 16 Slavic forms of unclear origin. Section 6 discusses eight Illyrian toponyms that were not borrowed into Slavic, but are helpful for the reconstruction of Illyrian phonology attempted in section 7.