Information has become a commonly-used tool in the apparatus of public authorities' intervention. Institutionally the management of air quality tends increasingly to be based on a set of devices of this kind. In France the December 1996 'Air Act'? and its various regulatory measures have promoted an obligation to inform the public in this respect. This article considers the implementation of prescriptions thus established, especially the outputs to which they are supposed to correspond. The idea is to illuminate the role of such information in the management of environmental problems. The analysis highlights the logics and tensions running through content in which the aim to inform is embodied, and characterizes the modalities of contact with the population via the different communication channels and mediums. It shows that this informative activity also involves an assimilation of the rules of the world of communication and the construction of credibility.