  We cross-correlate the cosmic microwave background temperature anisotropy
maps from the WMAP, MAXIMA-I, and MAXIMA-II experiments. We use the
cross-spectrum, which is the spherical harmonic transform of the angular
two-point correlation function, to quantify the correlation as a function of
angular scale. We find that the three possible pairs of cross-spectra are in
close agreement with each other and with the power spectra of the individual
maps. The probability that there is no correlation between the maps is smaller
than 1 * 10^(-8). We also calculate power spectra for maps made of differences
between pairs of maps, and show that they are consistent with no signal. The
results conclusively show that the three experiments not only display the same
statistical properties of the CMB anisotropy, but also detect the same features
wherever the observed sky areas overlap. We conclude that the contribution of
systematic errors to these maps is negligible and that MAXIMA and WMAP have
accurately mapped the cosmic microwave background anisotropy.
