  The CAIRNS (Cluster And Infall Region Nearby Survey) project is a large
spectroscopic survey of the infall regions surrounding nine nearby rich
clusters of galaxies. I describe the survey and use the kinematics of galaxies
in the infall regions to estimate the cluster mass profiles. At small radii,
these mass profiles are consistent with independent mass estimates from X-ray
observations and Jeans analysis. I demonstrate the dependence of mass-to-light
ratios on environment by combining these mass profiles with Two-Micron All-Sky
Survey (2MASS) photometry. Near-infrared light is more extended than mass in
these clusters, suggesting that dense cluster cores are less efficient at
forming galaxies and/or more efficient at disrupting them. At large radii,
galaxy populations in cluster infall regions closely resemble those in the
field. The mass-to-light ratio at these radii should therefore be a good probe
of the global mass-to-light ratio. The mass-to-light ratio in the infall region
yields a surprisingly low estimate of $\Omega_m \sim 0.1$.
