With this Special Issue "Development of the periodic system and its consequences" edited by Mary Virginia Orna and Marco Fontani, Substantia contributes to the celebrations of the 150^th anniversary of the periodic table.

Cover image: Transmitted polarized light micrograph (magnification 20x) from bisphenol-a crystallized from methanol, by John Atkinson, Union Carbide Corp., Bound Brook, New Jersey, USA. Courtesy of Nikon Small World (3^rd Place, 1979 Photomicrography Competition, https://www.nikonsmallworld.com).