  We present a measurement of the distant Type Ia supernova rate derived from
the first two years of the Canada -- France -- Hawaii Telescope Supernova
Legacy Survey. We observed four one-square degree fields with a typical
temporal frequency of <Delta t> ~ 4 observer-frame days over time spans of from
158 to 211 days per season for each field, with breaks during full moon. We
used 8-10 meter-class telescopes for spectroscopic followup to confirm our
candidates and determine their redshifts. Our starting sample consists of 73
spectroscopically verified Type Ia supernovae in the redshift range 0.2 < z <
0.6. We derive a volumetric SN Ia rate of r_V(<z>=0.47) = 0.42^{+0.13}_{-0.09}
(systematic) +- 0.06 (statistical) X 10^-4 yr^-1 Mpc^3, assuming h = 0.7,
Omega_m = 0.3 and a flat cosmology. Using recently published galaxy luminosity
functions derived in our redshift range, we derive a SN Ia rate per unit
luminosity of r_L(<z>=0.47) = 0.154^{+0.048}_{-0.033} (systematic)
^{+0.039}_{-0.031} (statistical) SNu. Using our rate alone, we place an upper
limit on the component of SN Ia production that tracks the cosmic star
formation history of 1 SN Ia per 10^3 M_sun of stars formed. Our rate and other
rates from surveys using spectroscopic sample confirmation display only a
modest evolution out to z=0.55.
