Clinical molecular genetics has only recently become recognizable as a diagnostic discipline in its own right-gradually becoming distinct from its academic-and research-based origins. This chapter seeks to give some shape and context to the contrtbutions that follow and add to previously published ideas of how diagnostic laboratories are structured and evolving (1, 2). The chapter largely draws on the UK experience of the field and does not claim to be authoritative on developments in North America, Europe, Australasia, or other parts of the world.