In the above sections some theoretical implications have been sprinkled in amongst the observations. The connection between DM and many cosmological problems is beyond the scope of the present article. (For a discussion of these issues, see papers in the proceedings edited by Barrow, Mestel and Thomas [1991]). However, there are a few issues which directly link DM with galactic properties and which are briefly discussed here. The most revolutionary of these, which would invalidate most of the conclusions that have been reached so far in this review, is that there is no DM at all around galaxies.