Dr. Pagel has given us a fine summary of the observations relevant to the topic I am to cover. Drs. Michaud and Vauclair have described in detail the potential effects of diffusive processes which might well explain, at least in part, the apparent abundance anomalies observed in the peculiar A stars and the magnetic A stars. In the paper following mine, Dr. Boesgaard will present the observational evidence regarding the abundance of the light elements lithium, beryllium and boron, and relate these observations to the theory of stellar envelopes. With these important topics expertly covered I shall restrict myself to the single question: How do some reasonably common types of stars, such as the carbon stars and the S stars, manage to show off at their surfaces, for us to observe, a fair sampling of the products of the nuclear burning going on deep in their cores?