The possible influence of CCN on cloud droplet size distributions and consequent radiation transfer remains a very active area of cloud physics research as the role of clouds in the radiative balance of the earth becomes increasingly recognized. The recent books entitled ``Aerosol-Cloud-Climate Interactions'' and ``Aerosol Effects on Climate'' edited by Hobbs [1993] and Jennings [1993] respectively, provide a good summary of present day knowledge of the possible influence of CCN and other aerosol particles on clouds and climate. The recent review by Hudson [1993] provides the current state of the art on Cloud Condensation Nuclei, and shows that CCN knowledge is still inadequate for understanding global climate change, and suggests that the knowledge base for CCN be significantly expanded.