HI and dark matter in spiral galaxies

We still do not have a "standard" model for the mass distribution of spiral galaxies. I review various methods used to delimit the range of values of the mass-to-light ratio of the disk, such as spiral structure criteria, the influence of bars, warped and flaring HI layers, velocity dispersions, and features in the rotation curve occuring just beyond the optical radius. It is not yet clear whether disks are maximal or not.