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 \sim 550 km s ^ { -1 } . A straightforward application of the virial theorem yields a group mass of 1.4 \times 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 .