In my thesis I would like to deal with vocabulary learning in relation to English as a Second Language. In the first chapter I intend to answer such questions as what is the importance of learning words and developing vocabulary. I intend to collect the results of various investigations, which serve as a background for estimations about the size of vocabulary of the native speakers, and about the desirable size of the vocabulary that learners should attain. I aim at focusing on the methods of the researchers concerned leading them to their results.