The concept active region, previously called ‘centre of activity’, was introduced by D'Azambuja as “the totality of all visible phenomena accompanying the birth of sunspots”. This idea was first placed in the centre of attention during the Convegno Volta in 1952 when Kiepenheuer put forward his paper: ‘Was ist ein Aktivitätszentrum auf der Sonne?’. At that time our knowledge of an active region could still be condensed in a five-page paper. During the present symposium we have listened to 89 communications, all dealing with certain aspects of the active region. Particular attention was given to the role played by supergranulation and by detailed magnetic fields; this was possible since we now have precise observations with good spatial and time resolution of the magnetic field, and very detailed information on the related optical structures.