The International Study of Asthma and Allergies in Childhood (ISAAC) is a collaborative research initiative aimed at investigating the increasing prevalence of asthma and allergic diseases in Western and developing countries. The study, which has attracted worldwide participation, consists of three phases: Phase 1 involves the use of standardized questionnaires to assess the prevalence and severity of asthma, rhinitis, and eczema in children across different centers and countries; Phase 2 focuses on investigating potential aetiological factors; and Phase 3 will repeat Phase 1 to monitor trends over time. The study aims to describe the prevalence and severity of these conditions, provide baseline measures for future trend assessments, and establish a framework for further research into genetic, lifestyle, environmental, and medical care factors affecting these diseases. The ISAAC initiative addresses the lack of standardized methods for measuring prevalence and severity and the absence of a coordinated research program for comparative data analysis. The study includes school children aged 6-7 and 13-14 years, with a sample size of 3,000 to ensure statistical power. The questionnaires cover wheezing, rhinitis, and eczema, and a video questionnaire is also used for 13-14 year olds. Data management and analysis will be conducted by the International Data Centre in Auckland, with results communicated to collaborators and further input sought. The organization of the study involves a Steering Committee, Regional Coordinators, National Coordinators, and Collaborating Centres, each with specific responsibilities.The International Study of Asthma and Allergies in Childhood (ISAAC) is a collaborative research initiative aimed at investigating the increasing prevalence of asthma and allergic diseases in Western and developing countries. The study, which has attracted worldwide participation, consists of three phases: Phase 1 involves the use of standardized questionnaires to assess the prevalence and severity of asthma, rhinitis, and eczema in children across different centers and countries; Phase 2 focuses on investigating potential aetiological factors; and Phase 3 will repeat Phase 1 to monitor trends over time. The study aims to describe the prevalence and severity of these conditions, provide baseline measures for future trend assessments, and establish a framework for further research into genetic, lifestyle, environmental, and medical care factors affecting these diseases. The ISAAC initiative addresses the lack of standardized methods for measuring prevalence and severity and the absence of a coordinated research program for comparative data analysis. The study includes school children aged 6-7 and 13-14 years, with a sample size of 3,000 to ensure statistical power. The questionnaires cover wheezing, rhinitis, and eczema, and a video questionnaire is also used for 13-14 year olds. Data management and analysis will be conducted by the International Data Centre in Auckland, with results communicated to collaborators and further input sought. The organization of the study involves a Steering Committee, Regional Coordinators, National Coordinators, and Collaborating Centres, each with specific responsibilities.