  At Run II of the Tevatron it will be possible to measure the W boson mass
with a relative precision of about 2 times 10^-4, which will eventually
represent the best measured observable beyond the input parameters of the SM.
Proper interpretation of such an ultrahigh precision measurement, either within
the SM or beyond, requires the meticulous implementation and control of higher
order radiative corrections. The FORTRAN package GAPP, described here, is
specifically designed to meet this need and to ensure the highest possible
degrees of accuracy, reliability, adaptability, and efficiency.
