Rock masses are distinguished from most other engineering materials by their inherently discontinuous nature and by the range of scales on which discontinuities occur within them. The paper highlights a number of concerns that these factors pose in engineering practice. It reviews the basic mechanics of discontinua and the historical development of the characterisation, testing and analytical and numerical techniques available to the engineer working with discontinuous rock. The practical application of these techniques is illustrated by examples of their use in underground construction, caving methods of mining and hot dry rock geothermal energy exploitation. Despite the difficulties that still arise in engineering in discontinuous rock masses, it is shown that quite remarkable advances have been made in the last 40 years.