This licentiate thesis explores the activity of historical reasoning in terms of primary source analysis among upper secondary school students. The thesis is a compilation of two scientific articles in history didactics. Two Learning studies, a theory-informed and interventionistic research methodology, were organised to explore historical reasoning. Three research questions are ad- dressed: (1) what does it mean to be able to analyse historical primary sources, (2) what is critical to discern when learning primary source analysis, and (3) what is characteristic for the processes of learning and meaning- making when students work with source analysis assignments? The first article uses phenomenography to explore fifteen students’ perceptions of a historical primary source and the difficulties they face when examining the source. Data was collected through a series of group interviews where stu- dents were asked to respond to a historical letter. The analysis resulted in four qualitatively different categories of perceptions of the source and three critical aspects that emerged between the categories. It is suggested that it is critical to (1) discern and separate the historical perspective, (2) to discern and separate the perspective of the historical actor and (3) to discern and separate the subtext of the source in relation to the historical context. The second article uses a form of content focused conversation analysis to ex- plore the processes of learning and attributing meaning when students work with primary sources. Data was collected through audio recordings of stu- dents’ collaborative work on two assignments. The main results are descrip- tions of the students’ learning and meaning making processes. For instance, when students discern and separate the historical perspective and historical actors’ perspectives. An interesting finding was a strategy used by students to take on the roles of hypothetical historical agents. It is suggested that cer- tain aspects of school culture might inhibit students’ learning of primary source analysis and that students’ life-world perspective is vital in creating meaning. Finally, historical reasoning is discussed in relation to the concept of historical consciousness and it is argued that historical reasoning should include the perspectives of deconstruction, subjectivity and interpretation to better comply with history teaching.