The analysis of canonical vacuum general relativity by R. Beig and N.Ó Murchadha (Ann. Phys. 174 463-498 (1987)) is extended in numerous ways. The weakest possible power-type fall-off conditions for the energy-momentum tensor of the matter fields, the metric, the extrinsic curvature, the lapse and the shift are determined which, together with the parity conditions, are preserved by the energy-momentum conservation law T ab ;b = 0 and the evolution equations for the geometry. The algebra of the asymptotic Killing vectors, defined with respect to a foliation of the spacetime, is shown to be the Lorentz Lie algebra for slow fall-off of the metric, but it is the Poincare algebra for 1/r or faster fall-off.It is shown that the applicability of the symplectic formalism already requires the 1/r (or faster) fall-off of the metric. The connection between the Poisson algebra of the Beig-Ó Murchadha Hamiltonians (and, in particular, the constraint algebra) and the asymptotic Killing vectors is clarified. Their Hamiltonian H[K a ] is shown to be constant in time modulo constraints for those asymptotic Killing vectors K a that are defined with respect to the foliation by the constant time slices.The energy-momentum and angular momentum are defined by the boundary term Q[K a ] in H[K a ] even in the presence of matter. Although the energy-momentum is well defined even for slightly faster than the r −1/2 fall-off, we show that the angular momentum and centre-of-mass are finite only if the metric falls off as 1/r or faster. Q[K a ] is constant in time for those K a 's that are asymptotic Killing vectors with respect to the foliation by the constant time slices. If the foliation corresponds to proper time evolution (i.e. its lapse tends to 1 at infinity), then Q[K a ] reproduces the ADM energy, the spatial momentum and spatial angular momentum, but the centre-of-mass deviates from that of Beig andÓ Murchadha by the spatial momentum times the coordinate time. The spatial angular momentum and the new centre-of-mass form an anti-symmetric Lorentz tensor, which transforms in the expected way under Poincare transformations. * Dedicated to Jim Nester on the occasion of his 60th birthday.1