In the case of multilingual learners it is not only the native language that influences their performance in their other languages, but also other previously learned languages. It is interesting to observe which of the learner's previous languages has more influence on the newly acquired language. The present study investigated the influence of the native language and a second language on a tertiary language. It compared the performances of Hungarian learners knowing German as a second language and English as a tertiary language, with that of learners knowing English as a second language. The goal was to find out whether a dissimilar native language or a similar second language was more helpful in the production of different linguistic features in English. These features were false cognates, prepositions, idioms and proverbs. The results have shown that not only the dissimilar native language Hungarian but also the similar language German was harmful in the performance of the learners. This book is for those who are interested in the influence of a native and a second language on a tertiary language.