The 48-inch Oschin Schmidt telescope at Palomar Observatory was used to obtain the first deep, optical, wide-field survey, covering almost two-thirds of the sky between November 1949 and December 1958 (with plates for the Whiteoak extension, to δc = −42°, taken in 1964/5). The original survey was taken in two passbands — wide blue and narrow red — on 103a emulsion, and covers one hemisphere in 643 fields with a spacing of 6 degrees between centres. In 1987, plate-taking started for the second Palomar Sky Survey, POSS II, which is intended to cover the northern hemisphere in three passbands, blue (IIIa-J + GG385 filter), red (IIIa-F + RG610) and near-infrared (IVN + RG9). Given the extremely restricted overlap between fields in the old survey, we have followed the example of the UK Schmidt ESO/SERC surveys and have adopted a 5-degree spacing between fields. To date (31.7.93), we have acquired plates of acceptable quality for 597 fields (67%) of the IIIa-J survey, 668 fields (75%) of the IIIa-F and 253 fields (28%) of the IVN.