*** This book was highly commended in the 2003 British Medical Association Book Competition*** During the past decade there have been major efforts to plan implement and sustain measures for reducing the burden of human disease that accompanies helminth infections. Further impetus was provided at the Fifty-fourth World Health Assembly when WHO Member States were urged to ensure access to essential anthelminthic drugs in health services located where the parasites - schistosomes, roundworms, hookworms, and whipworms - are endemic. The Assembly stressed that provision should be made for the regular anthelminthic treatment of school-age children living wherever schistosomes and soil-transmitted nematodes are entrenched. This book emerged from a conference held in Bali under the auspices of the Government of Indonesia and WHO. It reviews the science that underpins the practical approach to helminth control based on deworming. There are articles dealing with the public health significance of helminth infections with strategies for disease control and with aspects of anthelminthic chemotherapy using high-quality recommended drugs. Other articles summarize the experience gained in national and local control programmes in countries around the world. Deworming is an affordable cost-effective public health measure that can be readily integrated with existing health care programs; as such it deserves high priority. Sustaining the benefits of deworming depends on having dedicated health professionals combined with political commitment community involvement health education and investment in sanitation. " ... Let it be remembered how many lives and what a fearful amount of suffering have been saved by the knowledge of parasitic worms through the experiments of Virchow and others ... " - Charles Darwin, The Times 1881