  A summary is given of the calibration of the Cepheid scale required in the
derivation of distances from observations at V and I, as in the HST work on
extragalactic Cepheids. There is some evidence that a small metallicity
correction may be necessary in deriving distances in this way. The evidence for
this comes both from observations of Cepheids of different metallicities and
from a comparison of the LMC distance modulus derived from Cepheids and that
derived by other methods.
