  We present an expanded kinematic study of the young cluster NGC 2264 based
upon optical radial velocities measured using multi-fiber echelle spectroscopy
at the 6.5 meter MMT and Magellan telescopes. We report radial velocities for
695 stars, of which approximately 407 stars are confirmed or very likely
members. Our results more than double the number of members with radial
velocities from F{\H u}r{\'e}sz et al., resulting in a much better defined
kinematic relationship between the stellar population and the associated
molecular gas.
  In particular, we find that there is a significant subset of stars that are
systematically blueshifted with respect to the molecular ($^{13}$CO) gas. The
detection of Lithium absorption and/or infrared excesses in this blue-shifted
population suggests that at least some of these stars are cluster members; we
suggest some speculative scenarios to explain their kinematics. Our results
also more clearly define the redshifted population of stars in the northern end
of the cluster; we suggest that the stellar and gas kinematics of this region
are the result of a bubble driven by the wind from O7 star S Mon. Our results
emphasize the complexity of the spatial and kinematic structure of NGC 2264,
important for eventually building up a comprehensive picture of cluster
formation.
