The Plan of Selected Areas was suggested by the late Prof. J. C Kapteyn in 1906. The aim of the plan is to bring together, as far as possible, all the elements which seem most necessary for a successful attack on the problem of the structure of the sidereal world. The first, second and third reports on the progress of the plan were published by the Kapteyn Laboratory in 1909, 1910 and 1923 respectively, the fourth report appeared in Bulletin of the Astronomical Institutes of the Netherlands, No. 211, 1930. Many observatories and astronomers have co-operated on the plan and for the northern hemisphere most of the work has been finished or is now in progress.