The World Health Report 2002 a key purpose of this report is to provide governments with a strategy for that assess- ment as an avenue towards developing the best policies and an array of intervention op- tions for risk reduction. It also offers a comprehensive approach to the definition and study of risks In this report, risk assessment is defined as"a systematic approach to estimating the burden of disease and injury due to different risks". It involves the identification, quantification and characterization of threats to human health. Risk assessment can provide an invaluable, overall picture of the relative roles of different risks to human health; it can illuminate the potential for health benefits by focusing on those risks, and it can help set agendas fo research and policy action. The broader activity of risk analysis is a political activity as well as a scientific one and embraces public perception of risk, bringing in issues of values, process, power and trust. THE RISK TRANSITION In the general sense, many risks to health have, of course, already been reduced-and a few, such as smallpox, have been eliminated or eradicated. Much of the credit is due to the great progress in public health and medicine in the last century. Improvements in drinking- water and sanitation, the development of national health systems, the introduction of an- tibiotics and mass immunization against the causes of infectious diseases, and more recently better nutrition, are outstanding examples. Govemments, particularly in the last 100 years, have played the leading role in protecting and improving the health of their populations. As the 20th century ended, The World Health Report 1999 traced the revolutionary gains in life expectancy achieved in the previous few decades. These amounted to 30-40 years more life for people in some countries. Although the devastating impact of some diseases, such as HIVIAIDS, malaria and tuberculosis must be borne constantly in mind, it can still said that a substantial proportion of the world's population faces relatively low risk from most infectious diseases. However, although the risk factors considered in this report do not include pathogens such as bacteria, viruses and parasites, these continue to be leading contributors to ill-health. Other risk factors related to infectious diseases should not be overlooked. These include the growing problem of antimicrobial resistance, chronic infec tions that are associated with certain cancers, and the deliberate use of microbial agents to cause harm through terrorism or warfare. More generally, the generation and application of new knowledge about diseases and their control has played a vital role in improving the quality as well as the duration of life Decades of scientific research into the causes of disease and injury has given the world a vast knowledge base -now more widely accessible than ever before, thanks to the Internet and a huge potential for prevention and risk reduction. However, what is known, and what can be done, is not always reflected adequately in public health practice Meantime, while some risks to health have diminished, the very successes of the past w decades in infectious disease control and reduced fertility are inexorably generating a demographic transition"from traditional societies where almost everyone is young to sod eties with rapidly increasing numbers of middle-aged and elderly people the same time, researchers are observing marked changes in patterns of consump tion, particularly of food, alcohol and tobacco, around the world. These changing patterns are identified in this report as being of crucial importance to global health. They amount to thing less than a"risk transition"which is causing an alarming increase in risk factors in middle and low income countries4 The World Health Report 2002 A key purpose of this report is to provide governments with a strategy for that assess￾ment as an avenue towards developing the best policies and an array of intervention op￾tions for risk reduction. It also offers a comprehensive approach to the definition and study of risks. In this report, risk assessment is defined as “a systematic approach to estimating the burden of disease and injury due to different risks”. It involves the identification, quantification and characterization of threats to human health. Risk assessment can provide an invaluable, overall picture of the relative roles of different risks to human health; it can illuminate the potential for health benefits by focusing on those risks, and it can help set agendas for research and policy action. The broader activity of risk analysis is a political activity as well as a scientific one and embraces public perception of risk, bringing in issues of values, process, power and trust. THE RISK TRANSITION In the general sense, many risks to health have, of course, already been reduced – and a few, such as smallpox, have been eliminated or eradicated. Much of the credit is due to the great progress in public health and medicine in the last century. Improvements in drinking￾water and sanitation, the development of national health systems, the introduction of an￾tibiotics and mass immunization against the causes of infectious diseases, and more recently, better nutrition, are outstanding examples. Governments, particularly in the last 100 years, have played the leading role in protecting and improving the health of their populations. As the 20th century ended, The World Health Report 1999 traced the revolutionary gains in life expectancy achieved in the previous few decades. These amounted to 30–40 years more life for people in some countries. Although the devastating impact of some diseases, such as HIV/AIDS, malaria and tuberculosis must be borne constantly in mind, it can still be said that a substantial proportion of the world’s population faces relatively low risk from most infectious diseases. However, although the risk factors considered in this report do not include pathogens such as bacteria, viruses and parasites, these continue to be leading contributors to ill-health. Other risk factors related to infectious diseases should not be overlooked. These include the growing problem of antimicrobial resistance, chronic infec￾tions that are associated with certain cancers, and the deliberate use of microbial agents to cause harm through terrorism or warfare. More generally, the generation and application of new knowledge about diseases and their control has played a vital role in improving the quality as well as the duration of life. Decades of scientific research into the causes of disease and injury has given the world a vast knowledge base – now more widely accessible than ever before, thanks to the Internet – and a huge potential for prevention and risk reduction. However, what is known, and what can be done, is not always reflected adequately in public health practice. Meantime, while some risks to health have diminished, the very successes of the past few decades in infectious disease control and reduced fertility are inexorably generating a “demographic transition”from traditional societies where almost everyone is young to soci￾eties with rapidly increasing numbers of middle-aged and elderly people. At the same time, researchers are observing marked changes in patterns of consump￾tion, particularly of food, alcohol and tobacco, around the world. These changing patterns are identified in this report as being of crucial importance to global health. They amount to nothing less than a “risk transition” which is causing an alarming increase in risk factors in middle and low income countries