The proceedings of the 23 recorded air cleaning conferences since 1951 reflect an important aspect of the history of major nuclear developments, both military and civilian, because engineered safety features designed to prevent dispersion of radioactive products to the environment have always been a necessity for progress in this field. Each conference has recorded advancements in nuclear safety, and revealed the arrival of new challenges. The meetings have been a force for progress, as well as a forum for the refinement of current technology. The conferences will no doubt continue to be highly involved in the important tasks of maintaining and improving engineered safeguards for existing power reactors, and with meeting the air cleaning and treatment needs of advanced reactors.