Learners are active actors in learning environments and not mere consumers of instructional designers' products. In line with mediating paradigm instructional conceptions of students are analysed. These conceptions act as cognitive filters that affect students' use of both instructional interventions and support in learning environments. To gain insight in the complexity of students' instructional conceptions, the concept is analysed and its theoretical assumptions scrutinised. Next, research findings regarding instructional conceptions are reviewed. Attention is paid to the nature and development of students' instructional conceptions and to the relationship with similar conceptions. In the Discussion section, current limitations of both the conceptualisation and instrumentation of instructional conceptions are described and perspectives are opened on further research.