The idea of writing the present study was suggested to the author by the activities of the Council of Europe. Following an initiative of the Council's Committee of Ministers, colloquia on European law have been held since 1969 between the member countries of the Council under the auspices of its Secretariat. The first of these colloquia, held in London in 1969, related to a topic of private law. For another colloquium the Committee of Ministers chose a topic of public law appearing on the Council's agenda for the years 1971 and 1972, i.e., mutual assistance in administrative matters. The Secretariat invited the author of the present study to present areport on that topic at the colloquium which took pi ace at Aarhus, Denmark, from June 30th to July 2nd, 1971, under the Council's auspices. The present study contains the complete text, with some additions, of that report. What the author of this study wished to demonstrate is that joint solutions are conceivable in this sphere despite differing philosophical points of view and differing legal systems in the various member count ries of the Council of Europe. The author's special thanks go to the editors of Österreichische Zeitschrift für öffentliches Recht, Professor Verdross and Professor Zemanek, for their readiness to publish this study as a supplement to their journal. The author also thanks the publishers for the great understanding they have shown towards this project.