  We discuss some properties of the conjectured M-9-brane. We investigate both
the worldvolume action as well as the target space solution. The worldvolume
action is given by a gauged sigma model which, via dimensional reduction and
duality, is shown to be related to the worldvolume actions of the branes of
ten- dimensional superstring theory. The effective tension of the M-9-brane
scales as (R_{11})^3, where R_{11} is the radius of an S^1-isometry direction.
This isometry enables us to add a cosmological constant to eleven-dimensional
supergravity. The target space solution corresponding to the M-9-brane is a
(wrapped) domain wall of massive eleven-dimensional supergravity. This solution
breaks half of the bulk supersymmetry. We consider both single M-9-branes as
well as a system of two M-9-branes. In both cases one can define regions in
spacetime, separated by the domain walls, with zero cosmological constant. In
these regions the limit R_{11}-> \infty can be taken in which case the
M-9-brane is unwrapped and a massless eleven-dimensional supergravity is
obtained.
