  The discovery of high temperature superconductivity in cuprates was possible
only through an intimate knowledge of perovskite oxides which have been
synthesized and characterized for decades at the IBM in the Z\"urich
laboratoty. Especially SrTiO3 and LaAlO3 have been in the focus at IBM as was
presented in Volume 1 of a series [1]. Probably for the first time detailed
microscopic investigations of the local properties of these compounds have been
obtained by studying by means of EPR the surroundings of transition metal
impurities in these materials. These experiments enabled the identification of
the order parameter of the structural instability observed in these oxides.
However, the idea to search for superconductivity came later motivated by
theoretical considerations that metallic hydrogen could become superconducting
at high temperatures. Since SrTiO3 is an insulator it was thought that the
implantation of hydrogen would render it metallic and eventually also
superconducting. This approach failed since the carrier density remained always
too small. In sequence it was then tried to achieve a metallic state in oxide
perovskites by varying their composition which was in so far promising as
reduced SrTiO3 exhibits superconductivity at 0.3K [2]. Furthermore it was
subsequently shown [3] that Tc can be enhanced to 1.2K by doping SrTiO3 with
Nb. In spite of the fact that Tc was far below values achieved in A15
compounds, a remarkable observation was connected with the Nb doped perovskite,
namely for the first time long before predicted two-gap superconductivity was
realized here.
