  We present the maximally supersymmetric three-dimensional gauged
supergravities. Owing to the special properties of three dimensions --
especially the on-shell duality between vector and scalar fields, and the
purely topological character of (super)gravity -- they exhibit an even richer
structure than the gauged supergravities in higher dimensions. The allowed
gauge groups are subgroups of the global E_8 symmetry of ungauged N=16
supergravity. They include the regular series SO(p,8-p) x SO(p,8-p) for all
p=0,1,...,4, the group E_8 itself, as well as various noncompact forms of the
exceptional groups E_7, E_6 and F_4 x G_2. We show that all these theories
admit maximally supersymmetric ground states, and determine their background
isometries, which are superextensions of the anti-de Sitter group SO(2,2). The
very existence of these theories is argued to point to a new supergravity
beyond the standard D=11 supergravity.
