The use of ICT to enhance teaching and learning depends on effective design, which operates at many levels of granularity from the small to the very large. This reflects the range of educational problems from course design down to the design of activities focused on specific learning objectives. For maximum impact these layers of design need to be co-ordinated effectively. This paper delineates a reference model of 'layered learning design' where designs at one layer should use and incorporate designs from lower (more specific) layers in elegant and powerful ways. This would allow different designers, or tutors, to focus on different levels of abstraction in the learning design process, and to collaborate in combining designs to make a substantial impact on practice. The paper first delineates a model of the different layers of learning design. These layers range from the strategic structuring of learning activity (to achieve high-level goals) down to the design for basic learning activities. The paper then tackles the issue of the integration of this model with a major 'aggregation' model for learning objects. The essential insight is that learning objects should be viewed as instances of learning designs. This leads to a combined reference model where there is a correspondence between learning designs and learning object types at each layer. Finally, the paper applies the combined model to map some major contributions to learning design research and development.