This thesis focuses on the subject of vocabulary in English didactics. The main aim is to study the English vocabulary usage of upper secondary pupils in Norway. An analysis and comparison is made of Norwegian learners’ English to native speakers’ English. The material used for the analysis is a corpus of 50 written essays, 25 written by Norwegian upper secondary pupils and 25 written by American upper secondary pupils. Vocabulary analysis factors are used to help compare the texts produced by Norwegians learners of English and native English speakers. The comparison and analysis reveals some differences and similarities between these two groups. In addition, the study looks into how individual, frequent, varied, mature, and correct the English vocabulary that Norwegian language learners use in their free writing and how well prepared they are for further academic studies in English.