The present paper examines the factors influencing lexical transfer in third language acquisition (TLA) by examining studies devoted to lexical transfer from L1 and L2 into L3 that were mainly conducted in Europe. There are several factors that have influence on lexical transfer: linguistic (such as typology), contextual (such as naturalistic setting vs. formal setting), psycho-linguistic (such as psychotypology and the learners’ awareness of cognates), individual (such as learners’ age) and other factors (such as L2/L3 proficiency level). The results of the survey indicate that negative lexical transfer from both L1 and L2 to L3 occurs (a) in naturalistic contexts, (b) when languages are typologically similar, (c) when students perceive these languages as similar, and (d) when L2 proficiency level is high and L3 proficiency level low. In contrast, positive lexical transfer from L2 to L3 occurs (a) in formal settings, (b) when students perceive these languages as similar, (c) when learners’ awareness of true cognates is high, and (d) when both L2 and L3 proficiency level are high. Additionally, the learners’ age was found to potentially predict the relative weight of lexical transfer in TLA in the following manner: negative lexical transfer from L1 and L2 to L3 may increase with age. Finally, it was found that when L1, L2, and L3 are equally proximate, it is the L1 that has the primary influence on lexical transfer in TLA.