This study investigates the manifestation of Transfer or Cross-Linguistic Influence (CLI) from language learners’ previouslyknown languages in the learning of a third language, Northern Sotho, by examining errors identified in their written productions in the target language. Data for the study was gathered from first year university students learning Northern Sotho L3, with a roughly homogeneouslanguage background of isiZulu L1 and English L2 (elicitation tasks and questionnaires), and from three of their lecturers (interviews). The focus of the study was to determine whether the subjects produced patterns in their interlanguage that could be traced to one or both of their previously-known languages. Contrastive Analysis (CA) and Error Analysis (EA) techniques were used in the analyses of the learners’interlanguage (IL), to identify and quantify the errors, as well as to compare and contrast the three language systems at play in the learners’ minds, so as to pinpoint the possible source languages of the transfer. The findings indicate that most errors relating to spelling,vocabulary, and grammar, in general, showed evidence of prevalent influence from the language learners’ previouslyknown Black South African language (isiZulu L1), with no visible evidence of influence from English L2.