Expectations aside, the first step in the work of Bondi, Van der Burg, Metzner, and Sachs was to decide on some physically sensible boundary conditions to place on the gravitational field at light-like infinity to characterize what it means to say a metric is asymptotically flat, with no a priori assumptions made about the nature of the asymptotic symmetry group — not even the assumption that such a group exists. Then after artfully designing what they considered to be the most sensible boundary conditions, they investigated the nature of the resulting asymptotic symmetry transformations that leave invariant the form of the boundary conditions appropriate for asymptotically flat gravitational fields. What they found was that the asymptotic symmetry transformations actually do form a group and the structure of this group does not depend on the particular gravitational field that happens to be present. This means that, as expected, one can separate the kinematics of spacetime from the dynamics of the gravitational field at least at spatial infinity. The puzzling surprise in 1962 was their discovery of a rich infinite-dimensional group (the so-called BMS group) as the asymptotic symmetry group, instead of the expected ten-dimensional Poincaré group. The asymptotic symmetries include not only the six Lorentz boost/rotations but also an additional infinity of symmetries that are not Lorentz. These additional non-Lorentz asymptotic symmetries, which constitute an infinite superset of the four spacetime translations, are named supertranslations. This implies that General Relativity (GR) does not reduce to special relativity in the case of weak fields at long distances.