The aim of this thesis is to give an overview of the terminology and a summary of studies that have been done on genitive alteration. Both native and non-native English will be covered. The thesis features a forced choice questionnaire that was carried out with Estonian high school students to see their genitive choice. The results of the questionnaire are compared to the results of the same questionnaire carried out with native speakers of English. The first part of the thesis will introduce important terminology. Previous studies on genitive alteration with both native and non-native speakers will be analysed. The empirical part contains the forced choice questionnaire where the method is described and results are given as graphs. The third part will be the discussion of the results of the questionnaire, followed by the conclusion of this thesis.