The Powder Diffraction File (PDF®) is a collection of singlephase X-ray powder diffraction patterns in the form of inter-planar spacings (d) and relative intensities (I/I1), characteristic of the compound. Other information is included, when available, along with the references of the source information. The PDF® has been used for more than five decades and, as of 1992, contains about 67,000 patterns. The distribution and maintenance of the PDF® is carried out by the International Centre for Diffraction Data, located in Newtown Square, Pennsylvania. In the early days of the powder method, X-ray patterns were recorded on film, but the development of the powder diffractometer in the mid 1940s allowed the pattern to be recorded in a (generally) more useful analog trace form. However, because of storage considerations, in the case of both film and trace, it was necessary to “reduce” the experimental data to a d/I list. While the basic principle of the X-ray powder method has not changed too much during the last half century, there have been dramatic changes in the instrumentation used to record diffraction data, as well as in the data reduction methods used to produce the d/I lists which make up the core of the PDF®. This paper discusses the approaches taken by the ICDD to meet changing technology in maintaining the PDF® database in a way that is manageable, cost effective and, above all, satisfactory to a majority of the X-ray powder diffraction community.