Biogenic reefs are hard, compact structures created by the activity of living organisms. These structures create habitats and confer important ecological functions in the areas in which they occur. As a consequence they have been recognised by several legal frameworks which impart requirements for their management. Of the reefbuilding species in the UK, only three are likely to be of relevance to the marine aggregate industry: the ross worm Sabellaria spinulosa, the blue mussel Mytilus edulis and the horse mussel Modiolus modiolus. This monograph summarises the biology of these widely distributed species, the characteristics of the much rarer colonies that they form and the sensitivities of their reef structures to the potential impacts of aggregate dredging and other disturbances. Some of the management challenges of these habitats are also discussed, including the difficulties in their detection, sampling and mapping.