From population-based surveys around the world it is now clear that untreated cataract is by far the major cause of global blindness, accounting for over 20 million bilaterally blind people. Cataract is associated with ageing, but there appear to be several factors which increase the risk of an earlier onset. Until these risk factors are reduced by changes in life style or a specific preventive measure can be introduced, the treatment is by cataract surgery. A successful cataract service requires operating on sufficient numbers (output), good visual results (outcome) and adequate financial arrangements (outlay). Cataract surgery is the top priority of the new World Health Organisation Vision 2020 programme.