  In this thesis we summarize the reformulation of the bosonic sector of eleven
dimensional supergravity as a simultaneous nonlinear realisation based on the
conformal group and an enlarged affine group called G11. The vielbein and the
gauge fields of the theory appear as space-time dependent parameters of the
coset representatives. Inside the corresponding algebra g11 we find the Borel
subalgebra of e7, whereas performing the same procedure for the Borel
subalgebra of e8 we have to add some extra generators. The presence of these
new generators lead to a formulation of gravity including both a vielbein and
its dual. We review the arguments for the conjecture that the final symmetry of
M-theory should be described by a coset space, with the global and the local
symmetry given by the Lorentzian Kac-Moody algebra e11 and its subalgebra
invariant under the Cartan involution, respectively. The pure gravity itself in
D dimensions is argued to have a coset symmetry based on the very extended
algebra A^{+++}_{D-3}. The tensor generators of a very extended algebra are
divided into representations of its maximal finite dimensional subalgebra. The
space-time translations are thought to be introduced as weights in a basic
representation of the Kac-Moody algebra. Some features of the root system of a
general Lorentzian Kac-Moody algebra are reviewed, in particular those related
to even self-dual lattices.
