Considerable research has shown that the use of reading comprehension strategies (RCS) in the learning of second language (L2) has positive effects on students' reading comprehension (RC) performance. However, the development of L2 reading comprehension has been a challenge to Year 6 classes in Brunei that take place in an English as a foreign language (EFL) societal environment where both students and teachers have to achieve and work through English as a medium of instruction (EMI). In this complex environment, English reading comprehension amongst students in Brunei has been identified as an area that needs to be improved. The purpose of this study was to develop a deeper understanding of the complex relationships between the learning and teaching of RCS and the lived experience of Bruneian Year 6 students and teachers in EFL/EMI settings. This was achieved through an investigation of the facilitating or hindering factors involved in learning and teaching of RCS in L2 RC EFL/EMI classrooms, and an exploration of ways students and teachers manage EFL and EMI in the learning and teaching of RCS in L2 RC lessons. Engeström's Second Generation Activity Theory (2001) was used both as a theoretical framework and a method for analysis to generate a rich description of the complex environment in which the learning and teaching of RCS occurs.This study employed an instrumental case study using a sequential exploratory design and a mixed method approach. A total of 477 Year 6 students and 57 teachers participated in this study. In the first phase, data were collected from the students and teachers using RCS self-report surveys.This was followed by students undertaking a reading comprehension stimulation task, students' group interviews, teachers' interviews and classroom observations. Quantitative data were analysed using SPSS and thematic analysis was undertaken for the qualitative data.This study found that students and teachers were aware of the role of RCS in enhancing reading comprehension. However, the facilitating or hindering factors of EMI in EFL environment within an examination orientated education system such as students' perceived English competencies, limited instructional resources, and teacher directed pedagogical practices led to complexities in implementing RCS in the learning and teaching of L2 RC. The findings of this research provided evidence of some of the facilitators and hindrances of the learning and teaching of L2 RC, specifically the impact of EFL/EMI in the use of RCS in the bilingual classroom, and the ways students and teachers manage the learning and teaching of L2 RC within a complex system. This study further suggests that the learning and teaching of RCS in L2 RC lessons should be seen ii as complex as it is closely related to EMI policies in EFL setting within an examination orientated education system.The study adds to our understanding of RCS teaching and learning through the exploration of a context new to language learning strategies (LLS) research, that is, the use of...