  We present new BVRI broad-band photometry for the old open cluster NGC188
based upon analysis of 299 CCD images either obtained by us, donated by
colleagues, or retrieved from public archives. We compare our results on a
star-by-star basis with data from eleven previous photometric investigations of
the cluster. We homogenize and merge the data from all the photometric studies,
and also merge membership probabilities from four previous proper-motion
studies of the cluster field. Fiducial cluster sequences in the BV (Johnson) RI
(Cousins) photometric system of Landolt (1992, AJ, 104, 340) represent the
principal result of this paper. These have been compared to reference samples
defined by (a) Landolt's standard stars, (b) the old open clusters M67 and
NGC6791, and (c) stars within 25 pc having modern photometry and precise
Hipparcos parallaxes. In a companion paper we show that our derived cluster
results agree well with the predictions of modern stellar-interior and
-evolution theory, given reasonable estimates of the cluster chemical
abundances and foreground reddening. The individual and combined datasets for
NGC188 have been made available through our web site.
