The solar neutrino capture rate measured by the Russian-American Gallium Ex
periment (SAGE) on metallic gallium during the period January 1990 through
December 1997 is 67.2(-7.0-3.0)(+7.2+3.5) SNU, where the uncertainties are
statistical and systematic, respectively. This represents only about half o
f the predicted standard solar model rate of 129 SNU. All the experimental
procedures, including extraction of germanium from gallium, counting of Ge-
71, and data analysis, are discussed in detail. [S0556-2813(99)03510-4].