The purpose of this volume is to examine the concept and measurement of 'effectiveness', now increasingly employed to evaluate the kinds of operations where success cannot be judged in monetary terms. A philosopher comments on the development of the concepts of 'cause' and 'effect' from classical times to the present; a systems engineer looks at the possibility of using the parameter for the evaluation of coherent systems; a restoration ecologist discusses the parameters used in reforestation and their relation to effectiveness considered at different levels; a sociologist relates the methodologies used in this discipline to evaluate the effectiveness of health programs; an expert of education discusses the applicability of the measurement of effectiveness to the functioning of schools; a specialist in aid to developing countries describes the effectiveness of operations from the implementation of major projects to demining operations; a consultant on foreign aid highlights the cultural perception of efficacy in developing countries; finally, an anthropologist examines the relationship between 'effectiveness' and 'efficiency' in food intake and production between two different populations living in the same region, a semi-nomadic agro-pastoralist and a settled agriculturalist one. A concluding discussion notes the salience of the concept of effectiveness in many 'living' phenomena, including sociocultural ones, and the possibility of using them better to understand their evolution.