The work plan for the implementation of the Convention on Long-Range Transboundary Air Pollution under the UN Economic Commission for Europe (UN ECE) includes the production of maps of critical loads, critical levels, and exceedances as a basis for developing potential abatement strategies for sulphur and nitrogen. This Vademecum is designed to provide guidance to those responsible for calculating and mapping critical loads, critical levels, and exceedances on a national or regional scale. The chemical criteria and recommended methods to calculate critical loads and levels are described, together with elaboration of the chemical formulas to be used. These procedures were developed from several workshops and studies, which are referenced in the text. In addition, issues related to the practical aspects of producing maps, as well as statistical and uncertainty issues, are discussed.