  We show that the extremely low-mass white dwarf NLTT 11748 (0.17 M_sun) is in
a close binary with a fainter companion. We obtained a series of radial
velocity measurements of the low-mass white dwarf using the Halpha core and
determined an orbital period of 5.64 hours. The velocity semi-amplitude
(K=274.8 km/s) and orbital period imply that it is a degenerate star, and that
the minimum mass for the companion is 0.75 M_sun (assuming a mass of 0.167
M_sun for the primary). Our analysis of Balmer line profiles shows that a 0.75
M_sun white dwarf companion does not contribute more than 2% or 5% of the flux
(V-band) for helium- or hydrogen-rich surfaces, respectively. The kinematics of
the system suggest that it belongs to the Galactic halo.
