In recent decades pig production has been intensified in most European countries. This has resulted in a surplus of manure and a serious concern about the effect of ammonia emissions on environmental acidification and the pollution of ground and surface water. In the Netherlands, Denmark and France approximately 50% of the ammonia emissions from pig production is from pig housing and slurry storage. Ammonia emissions from pig houses can be reduced by: (1) lowering the concentrations of urea and ammonia in the slurry; (2) lowering the temperature of the slurry; (3) reducing the emitting surface area; (4) reducing the pH of the slurry. Various housing techniques have been developed to reduce ammonia emissions. Most of these techniques are costly but cheaper systems are becoming available. A combination of housing and feeding measures seems most promising to achieve a substantial reduction in ammonia emissions at relatively low costs. Lowering the protein content of the diet, including non-starch polysaccharides and adding acidifying salts instead of CaCO3 are the main possibilities at the moment to reduce the ammonia emission by dietary means.