This paper is concerned with the effects of local cold air on the thermal and air hygiene situation of urban areas. In order to determine these effects, it is necessary to analyse the meteorological conditions and processes underlying the production, dynamics and effects of cold air, to quantify the compensatory functions of these effects and to assess them in the light of human biometeorological aspects. Major factors which influence cold air are the topographic position and surface condition of producing areas, the allocation of these areas to areas of influence in the city, the availability of air flow paths to connect areas of production and influence and the structure (density) of the settlement edge. However, it is not intended to limit the analysis to solid surfaces but also to consider bodies of water (lakes, rivers and streams) are these often predominate in cities or lead from the surrounding countryside into an urban area. As local cold air flow is a key factor in town and country planning in Germany, VDI, the Asso-ciation of German Engineers, has decided to issue guideline. The objective of the guideline, which is to be drawn up by a committee of meteorologists, climatologists, engineers and planners, is to lay a standard physical foundation for argumentation using cold air as a planning factor and to ensure that cold air is given due consideration in planning at the local and regional level. The paper reports on the progress achieved to date.