This report has been prepared by the President with the assistance of the Vice-President, the Members of the Organizing Committee, V. V. Ivanov, P. Conti and of D. G. Hummer. The work of Commission 36 comes in contact with that of many commissions. Some subjects may be dealt with more fully in those reports; some subjects may have been “unlawfully” included here. Considerable choice has been exercised by the President about what to mention and in which section of the report to place it. The final product is only indicative of the large amount of work going on. An extensive bibliography has been compiled and will be distributed to commission members.

Commissions 12, 27, 29, 44 and 45 deal with observational material which our theories attempt to interpret, thus it is essential to study the reports of these commissions to appreciate the diversity of material for which theories are needed and against which theories may be checked. The theoretical treatment of the problems of planetary atmospheres, Commission 16, is not entirely divorced from that of stellar atmospheres. To set realistic inner boundary conditions on our atmosphere models and on our thinking, we must consider the material of Commission 35 while to set the outer boundary conditions we may consider the physical state of planetary nebulae which is one subject of Commission 34. When we wish to apply ideas about the interactions between radiation, atoms, ions and molecules we use material which lies in the province of Commission 14.