The GALLEX solar neutrino experiment, conducted at the Gran Sasso Underground Laboratories, used the inverse beta decay reaction $ {}^{71}\mathrm{Ga}(\nu_{e},\epsilon)^{71}\mathrm{Ge} $ to detect solar neutrinos. The experiment ran for 12 solar runs (GALLEX IV) from February 14, 1996, to January 23, 1997, with a total exposure time of 268 days. The result for GALLEX IV was $ [118.4 \pm 17.8 \, (\mathrm{stat.}) \pm 6.6 \, (\mathrm{sys.})] $ SNU (1σ), after subtracting contributions from side reactions and Rn-cut inefficiency. The combined result for GALLEX I-IV (65 solar runs) was $ [77.5 \pm 6.2 \, (\mathrm{stat.}) \pm 4.7 \, (\mathrm{sys.})] $ SNU (1σ). The results were consistent with a null result for the total of 36 blanks. The GALLEX experiment was followed by the Gallium Neutrino Observatory (GNO) in 1998. The results from the two Cr source experiments and the Arsenic experiments validated the GALLEX experiment and limited systematic biases to less than a few percent. The neutrino interaction rate was $ [77.5 \pm 7.7] $ SNU (1σ), which is substantially below the predictions of the various standard solar models. The result from the SAGE experiment agreed well with the GALLEX result. The GALLEX collaboration plans to prepare an extensive account of all of its experimental and theoretical activities in a concluding publication.The GALLEX solar neutrino experiment, conducted at the Gran Sasso Underground Laboratories, used the inverse beta decay reaction $ {}^{71}\mathrm{Ga}(\nu_{e},\epsilon)^{71}\mathrm{Ge} $ to detect solar neutrinos. The experiment ran for 12 solar runs (GALLEX IV) from February 14, 1996, to January 23, 1997, with a total exposure time of 268 days. The result for GALLEX IV was $ [118.4 \pm 17.8 \, (\mathrm{stat.}) \pm 6.6 \, (\mathrm{sys.})] $ SNU (1σ), after subtracting contributions from side reactions and Rn-cut inefficiency. The combined result for GALLEX I-IV (65 solar runs) was $ [77.5 \pm 6.2 \, (\mathrm{stat.}) \pm 4.7 \, (\mathrm{sys.})] $ SNU (1σ). The results were consistent with a null result for the total of 36 blanks. The GALLEX experiment was followed by the Gallium Neutrino Observatory (GNO) in 1998. The results from the two Cr source experiments and the Arsenic experiments validated the GALLEX experiment and limited systematic biases to less than a few percent. The neutrino interaction rate was $ [77.5 \pm 7.7] $ SNU (1σ), which is substantially below the predictions of the various standard solar models. The result from the SAGE experiment agreed well with the GALLEX result. The GALLEX collaboration plans to prepare an extensive account of all of its experimental and theoretical activities in a concluding publication.