The aim is to review the scientific and clinical principles of nebulized therapy and to produce a set of guidelines (evidence-based whenever possible) for users of nebulized treatment in Europe. It is hoped that the guidelines will improve clinical practice in the use of nebulized therapy throughout Europe. The most important considerations should be efficacy and patient safety. The guidelines will also serve as an educational and scientific resource for clinicians and scientists with an interest in inhaled therapy. These guidelines are aimed at a wide group of healthcare professionals practising in very different healthcare systems throughout Europe. The immediate target audience for the guidelines will be pulmonary physicians, but it is hoped that the messages will be communicated to all healthcare workers who are involved in treating patients with nebulized medication (doctors, nurses, pharmacists, paramedics, physiotherapists etc.).