͑MC͒ results are reported for the melting of two-dimensional systems of N hard disks in the NpT ensemble both for hard crystalline walls ͑for Nϭ900, 3844, and 15 876͒, and for periodic boundary conditions ͑for Nϭ64, 256, 400, 576, 1024, and 4096͒. Long Monte Carlo runs ͑e.g., up to 35ϫ10 6 MC sweeps for Nϭ15 876, and 2ϫ10 8 MC sweeps for Nϭ1024͒ give equilibrium results. We obtain mean values and fluctuations of the volume, of the orientational order parameter , and of the crystalline structure factor.Our main conclusions follow: ͑1͒ the melting transition is of second order; ͑2͒ ͗͘ drops discontinuously ͑from ͗͘ϭ0.74Ϯ0.02) to zero at the melting point; and ͑3͒ we find no hexatic phase ͑if it exists for systems of hard disks, then the range for it is within about 1% of the melting volume value͒. ͓S1063-651X͑97͒10201-X͔