This volume of the Handbook is the first of a two-volume set of reviews devoted to the rare-earth-based high-temperature oxide superconductors (commonly known as hiT C superconductors). The history of hiT C superconductors is a few months short of being 14 years old when Bednorz and Müller published their results which showed that (La,BA) 2 CuO 4 had a superconducting transition of ~30 K, which was about 7K higher than any other known superconducting material. Within a year the upper temperature limit was raised to nearly 100K with the discovery of an ~90K superconducting transition in YBa 2 Cu 3 O 7 - &dgr; . The announcement of a superconductor with a transition temperature higher than the boiling point of liquid nitrogen set-off a frenzy of research on trying to find other oxide hiT C superconductors. Within a few months the maximum superconducting transition reached 110 K (Bi 2 Sr 2 Ca 2 Cu 3 0 10 , and then 122K (TlBa 2 Ca 3 Cu 4 O 11 . It took several years to push T C up another 11 K to 133 K with the discovery of superconductivity in HgBa 2 Ca 2 Cu 3 O 8 , which is still the record holder today.