containing both bibliographic information and numerical data abstracted from the literature and relevant to molecular and crystal structures, as obtained by diffraction methods. The File is designed to permit the checking of published numerical values, particularly interatomic distances and bond angles and to present published results in a variety of new ways. Contents of the File will be made available through the series "Molecular Structures and Dimensions" and also by the provision of data on magnetic tapes or discs. At present the numerical data relating to molecular dimensions are being checked and will be published, at a later date, as further volumes in this series and also as magnetic tapes. The File is being extended to cover electron diffraction in the gas phase.