  In a number of multiply imaged quasar systems, a significant contribution to
the lensing potential is provided by groups and clusters of galaxies associated
with the primary lens. As part of an ongoing effort to gather observational
data on these systems, we present spectroscopy and near-infrared and optical
photometry of galaxies in the field of the quadruple lens system B 1422+231.
The spectra show that the primary lens and five nearby galaxies belong to a
compact group at z = 0.338. The median projected radius of this group is 35
h^{-1} kpc and its velocity dispersion is 550 km/s. A straightforward
application of the virial theorem yields a group mass of 1.4 x 10^{13} h^{-1}
M(sun), which provides sufficient external shear to produce the observed image
configuration. This data rules out a class of models and improves the system's
prospects for a measurement of the Hubble constant.
