  The rotation curves of dark matter dominated dwarf galaxies are analysed. The
observations show that dark matter halos represent a one-parameter family with
self similar density profiles. The global halo parameters, like total mass and
scale length are coupled by simple scaling relations. The inner halo regions
resemble non-singular, isothermal spheres with constant density cores. The
observations are compared with dark matter halos, resulting from cosmological
cold dark matter simulations. The theoretical models predict that dark matter
halos represent a one-parameter family in agreement with the observations.
However, in contradiction to the observations, the calculations lead to dark
matter halos with $r^{-1}$ density cusps in the center and non-isothermal
velocity dispersion profiles. Processes which might affect the inner halo
structure, resulting in isothermal, constant density cores are discussed.
