  Recent observations of Cepheids in the Virgo cluster have bolstered the
evidence that supports a Hubble constant in 70-90 km/s/Mpc range. This
evidence, by and large, probes the expansion of the Universe within 100 Mpc. We
investigate the possibility that the expansion rate within this region is
systematically higher than the true expansion rate due to the presence of a
local, large underdense region or void. We begin by calculating the expected
deviations between the locally measured Hubble constant and the true Hubble
constant for a variety of models. We also discuss the expected correlations
between these deviations and mass fluctuation for the sample volume. We find
that the fluctuations are small for the standard cold dark matter as well as
mixed dark matter models but can be substantial in a number of interesting and
viable nonstandard scenarios. However, deviations in the Hubble flow for a
region of radius 200 Mpc are small for virtually all reasonable models.
Therefore, methods based on supernovae or the Sunyaev-Zel'dovich effect, which
can probe 200 Mpc scales, will be essential in determining the true Hubble
constant. We discuss, in detail, the fluctuations induced in the cosmic
background radiation by voids at the last scattering surface. In addition, we
discuss the dipole and quadrupole fluctuations one would expect if the void
enclosing us is aspherical or if we lie off-center.
