  We have examined high accuracy radial velocities of Cepheids to determine the
binary frequency. The data are largely from the CORAVEL spectrophotometer and
the Moscow version, with a typical uncertainty of $\leq1$~km~s$^{-1}$, and a
time span from 1 to 20 years. A systemic velocity was obtained by removing the
pulsation component using a high order Fourier series. From this data we have
developed a list of stars showing no orbital velocity larger than
$\pm1$~km~s$^{-1}$. The binary fraction was analyzed as a function of
magnitude, and yields an apparent decrease in this fraction for fainter stars.
We interpret this as incompleteness at fainter magnitudes, and derive the
preferred binary fraction of $29\pm8$\% ( $20\pm6$\% per decade of orbital
period) from the brightest 40 stars. Comparison of this fraction in this period
range (1-20 years) implies a large fraction for the full period range. This is
reasonable in that the high accuracy velocities are sensitive to the longer
periods and smaller orbital velocity amplitudes in the period range sampled
here. Thus the Cepheid velocity sample provides a sensitive detection in the
period range between short period spectroscopic binaries and resolved
companions. The recent identification of $\delta$ Cep as a binary with very low
amplitude and high eccentricity underscores the fact that the binary fractions
we derive are lower limits, to which other low amplitude systems will probably
be added. The mass ratio (q) distribution derived from ultraviolet observations
of the secondary is consistent with a flat distribution for the applicable
period range (1 to 20 years).
