  This is the fifth and final summary paper of our 15 year program using the
Hubble Space Telescope (HST) to determine the Hubble constant using Type Ia
supernovae, calibrated with Cepheid variables in nearby galaxies that hosted
them. Several developments not contemplated at the start of the program in 1990
have made it necessary to put the summary on H_0 on a broader basis than
originally thought, making four preparatory papers necessary. The new Cepheid
distances of the subset of 10 galaxies, which were hosts of normal SNeIa, give
weighted mean luminosities in B, V, and I at maximum light of -19.49, -19.46,
and -19.22, respectively. These calibrate the adopted SNeIa Hubble diagram from
Paper III to give a global value of H_0 = 62.3 +/- 1.3 (random) +/- 5.0
(systematic). Local values of H_0 between 4.4 and 30 Mpc from Cepheids, SNeIa,
21cm-line widths, and the tip of the red-giant branch (TRGB) all agree within
5% of our global value. This agreement of H_0 on all scales from 4 - 200 Mpc
finds its most obvious explanation in the smoothing effect of vacuum energy on
the otherwise lumpy gravitational field due to the non-uniform distribution of
the local galaxies. The physical methods of time delay of gravitational lenses
and the Sunyaev-Zeldovich effect are consistent (but with large errors) with
our global value. The present result is also not in contradiction with existing
analyses of CMB data, because they either lead to wide error margins of H_0 or
depend on the choice of unwarrented priors that couple the value of H_0 with a
number of otherwise free parameters in the CMB acoustic waves. Our value of H_0
is 14% smaller than the value of H_0 found by Freedman et al. (2001) because
our independent Cepheid distances to the six SNeIa-calibrating galaxies used in
that analysis average 0.35mag larger than those used earlier.
