This paper describes the broad field of interactional aerodynamic phenomena, classifies the problems into logical categories, and establishes a matrix of interactions and problems. A structured basis is thereby provided for systematic problem identification and interaction analysis according to needs and priorities. Specific interactions are analysed where sufficient data is available. These include the rotor/hub/fuselage/empennage, rotor/fuselage/ground, and tail rotor/main rotor/ground interactions. The evident trends are discussed and conclusions are drawn regarding significant physical mechanisms. Finally, further research is recommended to expand the database, to foster theory development and to develop  meaningful design guidelines. The meager state of the art in this field of demonstratred major problems presents a new challenge to helicopter aerodynamic technology, which until now has emphasized the isolated rotor in research and development.