CCD photometry and astrometry for visual double and multiple stars of the HIPPARCOS catalogue I. Presentation of the large scale project

A description is given of the activities of an international working group created with the aim of obtaining both photometric and astrometric observat ions of visual double and multiple stars with angular separations in the ra nge of one to fifteen arcseconds, that formed part of the HIPPARCOS Input C atalogue. The scientific aims and realisations of this European network an given. About 50 observational missions have been carried out in both hemisp heres according to a pre-defined protocol. We describe the general and spec ifically designed methods used for the reduction of large amounts of CCD ob servations of double stars and give an outline of the results already prese nted and soon to be expected.