Inquiry-based instruction is an important teaching strategy in science education that can be implemented to achieve different learning goals (e.g. the learning of science content or of inquiry skills and strategies). Inquiry-based instruction is often combined with guidance attempting to assist students to effectively engage in inquiry activities and, through this engagement, reach the intended goals. In recent research, the type and amount of guidance needed to foster student's learning has received considerable attention. One challenge in interpreting the results of this line of research is the manifold meanings of the term 'guidance' and its implementation in inquiry-based instruction. Moreover, the effectiveness of a particular type and amount of guidance may also depend on the learning goal that is to be achieved. In this paper, we draw on existing research and theoretical considerations in attempting to disentangle three major dimensions in which the implementation of guidance may vary: (a) the degree of autonomy, (b) the degree of conceptual information, and (c) the cognitive domain of guidance. We discuss how these dimensions can be used to capture and systemise findings of existing studies as well as to infer desiderata for further research on the role of guidance in inquiry-based instruction.