One of the major issues facing science, engineering and technology (SET) around the world today relates to the decline of young people, especially women, enrolling in these subjects and entering careers in these fields. This will have tremendous consequences for capacity in science and engineering, particularly in developing countries -where SET applications are vital in social and economic development and in addressing the Millennium Development Goals (MDGs), especially poverty reduction and sustainable development. Capacity in SET is further weakened by brain drain to developed countries.These issues of capacity and the application of SET to development relate closely to considerations of diversity, access, equity, participation and career development for women in science and engineering. Women are under-represented in all areas of engineering, mathematics, physics and chemistry in most countries around the world. We need to get more women and under-represented groups into SET to promote social and economic development. The situation at the tertiary and professional levels reflects the decline in young people's, especially women's, interest in SET education at primary and secondary school. Children turn away from science and technology (S&T) in the later primary and early years of secondary education -that is where the problem begins.Indicators and information are required in many countries to help understand and address this situation of declining interest in and entry into science and engineering, and the consequences thereof for capacity and application of SET for social and economic development. We need data and information for evidence-based analysis and understanding of the situation, and for policy-making and planning to address the problem. The situation is compounded in developing countries by the shortage of statistics and indicators on science and engineering.The production of this UNESCO toolkit on gender indicators in SET is therefore a welcome, timely and indeed overdue contribution to this field. Calls for greater information on and action towards women and gender issues in science and engineering have been made at UNESCO General Conferences for over twenty years, and were a priority of the Framework for Action of the World Conference on Science in 1999. UNESCO commissioned the production of this volume to address these calls. The toolkit introduces the subject, discusses the need for gender indicators in SET to counter the 'leaky pipeline' of women into and within science and engineering, surveys the measurement of people and activities in SET, and provides case studies of the collection and analysis of gender-disaggregated data.The authors, Sophia Huyer and Gunnar Westholm, are specialists on gender issues and indicators in SET, and UNESCO is proud to have been involved in the production of the first publication focusing on this field. We look forward to the contribution that this toolkit on gender indicators in SET will make to the information, policy-making and planning required to address t...