The main criterion for election as a TWAS Member is scientific excellence. Only those scientists who have attained the highest international standards and have made significant contributions to the advancement of science can be nominated as Fellows or Associate Fellows.
Fellows are scientists who live and work in developing countries and who have made contributions to their fields of science that meet internationally accepted standards of excellence;
Associate Fellows are scientists who live and work in developed countries, have made contributions to their fields of science that meet internationally accepted standards of excellence, and, additionally, have distinguished themselves in efforts to promote science in developing countries.
Eighty-six percent of TWAS Members are Fellows, fourteen percent are Associate Fellows. Members are elected for life.
(引用：http://twas.ictp.it/mbrs/mbrs-general)
