Thousands of papers in the field of radio astronomy have appeared during the last three years. Even simple enumeration of the major achievements will take much more space than it has been allocated to Commission 40. Therefore, taking into account the tendency of the previous years, much greater attention in the present report has been paid to the actual material and references (mainly of observational and methodological character). As to the interpretation of observations, much overlapping has occurred with Commissions 10 and 34. Solar radio astronomy had to be excluded from the report of Commission 40 in view of its practically complete overlapping with the report of Commission 10. Physical interpretation of insterstellar medium observations carried out by radio techniques during the three years has been included in the report of Commission 34. Even in this case we have been forced, as in the previous years, to introduce some additional abbreviations of the most widely used journals in the sections containing a great number of references. These abbreviations are given below.

Commission 44 is by title technique oriented. The following statement of the role of the commission was prepared for use by the General Secretary in responding to requests by non-astronomers with respect to the activities of IAU commissions.

‘The Earth’s atmosphere is opaque to radiation throughout most of the electromagnetic spectrum. The light reaching the surface of the Earth from celestial objects is confined primarily to the visual region of the spectrum and a larger window in the radio region. Much of the infrared and all the far ultraviolet, X-ray and γ-ray radiation are absorbed in the upper atmosphere. Thus astronomers must carry their telescopes and auxiliary instrumentation above the Earth’s atmosphere to unlock the clues on the structure of the universe revealed by the light at these wavelengths. Furthermore the light in the accessible region of the spectrum that does reach the surface of the Earth is distorted and scattered in such a manner that the spatial resolution and details of the radiating source is seriously degraded.

In view of the broad range of topics covered by Commission 48, and the consequent inevitable overlap with other commissions, it is not feasible to produce a comprehensive self-contained report. The commission therefore decided to restrict its report to a selected list of accessible recent review articles and conference reports, wherein up-to-date summaries of various topics can be found. Such a list is given below: