The topic of learning foreign languages is still urgent; moreover, it is getting more and more significant for a thriving number of teachers, methodologists and philologists. The main issue of these researches is that the results will provide the learners with the most effective and useful strategies and ways for acquiring a foreign language. The article gives the definition of the term interference and identifies its role in foreign languages learning. The key methods used in our article are analysis, synthesis, and comparative analysis. It studies constructive and destructive impact of interference in learning two foreign languages: English and German. There are the examples demonstrating positive and negative effects of one language on the other at the different language levels. The result of the research has both theoretical and practical value as it can be used to make up and implement the programs for learning foreign languages as well as to use them in practical classes.