The aim of the present review is to report the state of the art of an emerging family of molecules, namely 4-substituted spirobifluorenes (SBFs). Their syntheses, physico-chemical and photophysical properties and applications as hosts in Phosphorescent Organic Light-Emitting diodes (PhOLEDs) are described through a structure–property relationship approach. Although substitution at position 2 of a SBF core has been widely developed, substitution at position 4 is very recent (less than 10 years) and stills need to be explored.