Long before any Slavic languages were first attested, speakers of what would become the Slavic languages came into contact with speakers of a northern Iranian language usually called Scythian. Iranian loanwords in the Slavic languages show us that as they moved into the same regions of Eastern Europe, the Scythians and the Pre-Proto-Slavs had significant contact, probably in the form of a primarily trade-based relationship; while some religious terminology is shared, it is no more than we would expect from any two cultures in contact over a long time. This thesis explores the Iranian loanwords which can be found in the attested Slavic languages and what they imply about the nature of contact between these groups.