  We present the first measurement of the rate of Type Ia supernovae at high
redshift. The result is derived using a large subset of data from the Supernova
Cosmology Project as described in more detail at this meeting by Perlmutter et
al. (1996). We present our methods for estimating the numbers of galaxies and
the number of solar luminosities to which the survey is sensitive, the
supernova detection efficiency and hence the control time. We derive a
rest-frame Type Ia supernova rate at z~0.4 of 0.82^+0.54_-0.37 ^+0.42_-0.32 h^2
SNu where the first uncertainty is statistical and the second includes
systematic effects.
