This review article is a commemoration of the 30th anniversary of the discovery of YBa 2 Cu 3 O 7-d high-temperature superconductors (HTSCs). As a result of this discovery a family of (RE)Ba 2 Cu 3 O 7-d (RE stands for "rare earth") HTSCs has found great practical use. The review article consists of a brief history of how YBa 2 Cu 3 O 7-d was conceived and five sections describing the family of compounds: crystallography, phase diagrams, manufacturing techniques, main superconducting properties, and fields of application.