This report briefly describes the sources of emissions of ammonia gas and their impact on the environment, on the cycle and use of nitrogen in the soil and on human and animal health. It provides an overview of research conducted to develop and evaluate techniques for reducing ammonia emissions, in order to identify those that are the most cost-effective and widely applicable. Current policies to solve this problem, used in five countries (the Netherlands, Denmark, the United Kingdom, Sweden and Germany) are defined. Options are considered on the basis of the MARACCAS model (Model for the Assessment of Regional Ammonia Cost Curves for Abatement Strategies).