In an astronomical subject of such wide applications as interstellar dust it is to be expected that not only are there diverse opinions on its precise nature, but also diverse opinions on its influence in various astrophysical environments. At this Enrico Fermi school lecturers of the highest calibre presented their subjects and points of view to the students, so that the basic scientific controversies and methodology were accessible. In addition to questions of sources and growth, the destruction of grains was extensively discussed. A number of physical processes, such as charging and heating of grains, were also considered. Classically, and in the current context of dust problems, the optics of grains individually and in clouds has been the most critically and fully treated aspect.