A sound appreciation of the biology of coral habitats must be grounded in understanding both the geological and hydrographic contexts in which these habitats have developed. As sessile, structure-forming species dependent on water flow to supply food, exchange gametes and disperse larvae, corals are intimately related to near-seabed hydrography and, in turn, their occurrence on continental shelves, slopes and seamounts may help interpret flow and turbulence regimes in these dynamic regions of the world's oceans. In this chapter, we consider both the structural and functional biology of the major groups of cold-water corals described in Chapter 2. We outline the major hypotheses that have been advanced to explain coral occurrence and review currently available evidence. Finally, and perhaps most significantly, we note that many aspects of the basic biology of cold-water corals are either unknown or have only been examined very recently. For this reason elements of the chapter will necessarily be brief but will include notes on where we can expect advances as the scientific community capitalises on our improved geological understanding of cold-water coral distribution and occurrence and begins to address fundamental questions on seasonality, food supply, ecophysiology, growth and reproduction.