The Flexible Image Transport System (FITS) evolved out of the recognition that a standard format was needed for transferring astronomical data from one installation to another. The original form, or Basic FITS , was designed for the transfer of images and consisted of a binary array, usually multidimensional, preceded by an ASCII text header with information describing the organization and contents of the array. The FITS concept was later expanded to accommodate more complex data formats. A new format for image transfer, random groups, was defined  in which the data would consist of a series of arrays, with each array accompanied by a set of associated parameters. These formats were formally endorsed  by the International Astronomical Union (IAU) in 1982. Provisions for data structures other than simple arrays or groups were made later. These structures appear in extensions, each consisting of an ASCII header followed by the data whose organization it describes. A set of general rules governing such extensions  and a particular extension, ASCII table , were endorsed by the IAU General Assembly  in 1988. At the same General Assembly, an IAU FITS Working Group (IAUFWG) was formed  under IAU Commission 5 (Astronomical Data) with the mandate to maintain the existing FITS standards and to review, approve, and maintain future extensions to FITS, recommended practices for FITS, implementations, and the thesaurus of approved FITS keywords. In 1989, the IAUFWG approved a formal agreement  for the representation of floating point numbers. In 1994, the IAUFWG endorsed two additional extensions, the image extension  and the binary table extension . FITS was originally designed and defined for 9-track half-inch magnetic tape. However, as improvements in technology have brought forward other data storage and data distribution media, it has generally been agreed that the FITS format is to be understood as a logical format and not defined in terms of the physical characteristics of any particular data storage medium. In 1994, the IAUFWG adopted a set of rules  governing the relation between the FITS logical record size and the physical block size for sequential media and bitstream devices. The IAUFWG also approved in 1997 an agreement  defining a new format for encoding the date and time in the DATE, DATE-OBS, and other related DATExxxx keywords to correct the ambiguity in the original DATE keyword format beginning in the year 2000.