The dissertation is a contrastive analysis. It deals with the acquisition of English relative clause (RC) by German and Turkish students(in Germany and Turkey) learning English as a second and third language and attending the 11th grades of a German school. The main question of the study is to find out whether the acquisition of English RCs is more difficult for German or for Turkish learners. The other study is the corpus analysis of the English relative clauses. For this research (...) I have chosen various school books from the fields such as History, Chemistry and Literature. The target is to find out how often the English relative clauses are used. They are from the same school level (11th grade) where I have applied the tests. I wanted to know which difficulties exists for the students. Moreover the frequency of English relative clauses in the school books has been given. (shrink)