  I present recent progress in theoretical modelling of cosmological
density--velocity relations in the weakly nonlinear regime. The relations are
local, based on rigorous perturbation theory and include the effects of
smoothing of the density and the velocity fields. For small smoothing scales,
they can be improved by slight adjustments based on N-body results. The
relations can be useful for density--velocity comparisons, yielding a fair
estimate of Omega and offering a method for disentangling Omega and bias.
