This publication collates the proceedings of the Workshop on Demonstration of Equivalence between Ambient Air Monitoring Methods, which was held at the JRC in Ispra (VA) from 2 - 4 May 2007 and the major discussions vis-à-vis the last version of the Guideline on demonstration of Equivalence . The extensive use by national reference laboratories of this guideline strengthens the principles on which the current guideline is based.