  AdS2 has an SL(2,R) isometry group. It is argued that in the context of
quantum gravity on AdS2 this group is enlarged to the full infinite-dimensional
1+1 conformal group. Massive scalar fields are coupled to AdS2 gravity and
shown to have associated conformal weights h(m) shifted by their mass. For
integral values of h primary boundary operators are obtained as h normal
derivatives of the scalar field. AdS2 string theories arise in the
`very-near-horizon' limit of S1-compactified AdS3 string theories. This limit
corresponds to energies far below the compactification scale. The dual
conformal field theory has one null dimension and can in certain cases be
described as the discrete light cone quantization of a two-dimensional deformed
symmetric-product conformal field theory. Evidence is given that the AdS2
Virasoro algebra is related to the right-moving AdS3 Virasoro algebra by a
topological twist which shifts the central charge to zero.
