The present licentiate thesis aims to investigate pupils’ understanding and use of teacher written feedback in English as a foreign language (EFL). The study was carried out in two Swedish lower secondary schools in two different classrooms, one in year eight with 14-year-old pupils and one in year nine with 15-year-old pupils. A case study research design was adopted to gain insights into nine pupils’ understand-ing and use of feedback. The three participants in year eight wrote ‘a letter to Barack Obama’ and received teacher written feedback in their draft texts and on a separate paper with individualized comments. The six pupils in year nine wrote about ‘mov-ies’ and received teacher written feedback in their draft texts but were also provided with a writing checklist. Data were collected from multiple sources but the data used for analysis were comprised of pupils’ draft and final version texts and pupil reflec-tive interviews.  The findings suggest that pupils understand many of the issues addressed by the teachers in their written feedback. Most pupils express their understanding using everyday language and by resorting to different strategies such as explaining why the feedback is provided, suggesting adequate changes or just by providing a correc-tion. However, it seems hard for a few pupils to understand the use of implicit types of written feedback. The results of the present study also suggest that it is hard to know a priori what pupils will experience as difficult to understand when it comes to the language used by the teachers in their written explanations. The findings further show that the majority of feedback points trigger pupils to make revision operations that involve major text-based changes. In other words pupils make more changes than those addressed in the teachers’ written feedback. The results also highlight that most pupils do not challenge their teachers’ feedback.  The findings of this study contribute to research on foreign language (FL) writing by providing insights from pupils’ perspectives and may fill a gap in the field of FL writing, since there are not many studies based on pupils’ perceptions. The context in which this study took place, lower secondary level and EFL in Sweden, also makes an additional contribution to the field of FL writing.