The Advanced Research Institute on "Health Services Systems" was held under the auspices of the NATO Special Programme Panel on Systems Science as a part of the NATO Science Committee's continuous effort to promote the advancement of science through international cooperation. A special word is said in this respect supra by Pro- fessor Checkland, Chairman of the Systems Science Panel. The Advanced Research Institute (ARI) was organized for the purpose of bringing together senior scientists to seek a consensus on the assessment of the present state of knowledge on the specific topic of "health services systems" and to present views and recom- mendations for future health services research directions, which should be of value to both the scientific community and the people in charge of reorienting health services. The conference was structured so as to permit the assembly of a variety of complementary viewpoints through intensive group discussions to be the basis of this final report. Invitees were selected from allover Europe and North America, including observers from the major international organizations involved in health ser- vices research, to provide the experience and expertise necessary to make the issue of "health services systems" val id and significant.