  The research on relativistic universe models with viscous fluids is reviewed.
Viscosity may have been of significance during the early inflationary era, and
may also be of importance for the late time evolution of the Universe. Bulk
viscosity and shear viscosity cause exponential decay of anisotropy, while
nonlinear viscosity causes power-law decay of anisotropy. We consider also the
influence from turbulence, in connection with future singularities of the
universe (Big Rip and Little Rip). Finally, we review some recent developments
of causal cosmology theories.
