matter associated to galaxies represents a small fraction of the mass density of the universe, and that galaxies may be biased relative to the underlying distribution of matter. Still, if structures grow as a result of gravity alone, observation of the peculiar velocity of galaxies provides the means to probe the distribution of the total matter. In the standard picture for the formation of cosmic structures via gravitational instability the peculiar velocity of a galaxy is generated by fluctuations in the mass distribution. For galaxies outside virialized systems, linear perturbation theory predicts $$\vvec (\rvec) \approx {\Omega^{0.6}H_o \over 4\pi} \int{ d^3r^\prime \delta_m
{(\rvec^\prime - \rvec) \over \vert \rvec^\prime - \rvec \vert ^3}} \; .
\label{lingrav}$$ This can also be expressed in the following differential form $$\nabla \cdot {\bf v} = -\Omega^{0.6} \delta_m,
\label{divv}$$ where $\Omega$ is the mass density parameter, $H_o$ is the Hubble constant and $\delta_m$ is the mass density fluctuation field. If galaxies are fair tracers of the underlying mass distribution and galaxy biasing is linear then $\delta_g = b \delta_m$, where $\delta_g$ is the galaxy density contrast and $b$ is the bias parameter for a given population of mass tracers. The above equations show that by mapping the 