The human genome project is the largest focussed project ever undertaken in human biology. Its initial aims were to determine the sequence of the 3 billion organic bases which form the genetic code, and to identify all genes. The draft version of the sequence was published in February 2001. Perhaps the most surprising outcome of this was the finding that humans have only have around 35,000 genes, fewer than early estimates had suggested. Approximately 75% of the genome is ‘intergenic’ with 25% forming the components of genes. The advent of the sequence will allow the ready isolation of genes for rare diseases much more rapidly than in the past. The project will not be completed until the functions of all genes and their roles in human health and disease have been determined. The common variant forms of all genes should be known by about 2003. Arising from this will be knowledge of the interactions of an individual’s genome with the environment and this will reveal susceptibility to common diseases. Predictive medicine will be the ability to determine, from genetic testing, those diseases which an individual has increased risk of developing later in life. Knowledge of the genes involved in disease susceptibility will provide a range of new targets for the development of drugs to prevent and treat disease. Testing for susceptibility genes for common diseases will allow specific strategies to be developed to delay their onset, and new drugs will be developed to allow specific treatments.