  The lack of radial velocity data in the Hipparcos catalogue was considered a
significant deficiency, so when Gaia was conceived, a spectrometer was a core
constituent of its payload. The Gaia Radial Velocity Spectrometer faced a
number of design challenges, in particular set by the need to balance kinematic
and astrophysical capability. We present an overview of the evolution of the
instrument to its present form, identifying the competing technical,
performance and programmatic factors which have shaped it.
