  We present a measure of the hard (2-8 keV) X-ray luminosity function (XLF) of
Active Galactic Nuclei up to z~5. At high redshifts, the wide area coverage of
the Chandra Multiwavength Project is crucial to detect rare and luminous (Lx >
10^44 erg s^-1) AGN. The inclusion of samples from deeper published surveys,
such as the Chandra Deep Fields, allows us to span the lower Lx range of the
XLF. Our sample is selected from both the hard (z < 3; f(2-8 keV) > 6.3x10^-16
erg cm^-2 s^-1) and soft (z > 3; f(0.5-2.0 keV) > 1.0x10^-16 erg cm^-2 s^-1)
energy band detections. Within our optical magnitude limits (r',i' < 24), we
achieve an adequate level of completeness (>50%) regarding X-ray source
identification (i.e., redshift). We find that the luminosity function is
similar to that found in previous X-ray surveys up to z~3 with an evolution
dependent upon both luminosity and redshift. At z > 3, there is a significant
decline in the numbers of AGN with an evolution rate similar to that found by
studies of optically-selected QSOs. Based on our XLF, we assess the resolved
fraction of the Cosmic X-ray Background, the cumulative mass density of
Supermassive Black Holes (SMBHs), and the comparison of the mean accretion rate
onto SMBHs and the star formation history of galaxies as a function of
redshift. A coevolution scenario up to z~2 is plausible though at higher
redshifts the accretion rate onto SMBHs drops more rapidly. Finally, we
highlight the need for better statistics of high redshift AGN at z > 3, which
is achievable with the upcoming Chandra surveys.
