This symposium volume, containing 22 chapters (of which 19 are based on 16 invited and 3 short lectures, all delivered by distinguished and internationally recognized scientists from 8 countries), is a monograph on the most recent progress in the chemistry of rings and clusters of the main group elements (from boron via carbon, silicon, germanium, tin, nitrogen, phosphorus and arsenic, to sulfur and selenium, excluding the heaviest ones). It is organized by elements, moving from left to right in the main groups of the Periodic Table, followed by one chapter each on bonding and nomenclature of ring molecules.