  We give a concise review of recent developments of the M5-brane theory
derived from the Bagger-Lambert model. It is a 6 dimensional supersymmetric
self-dual gauge theory describing an M5-brane in a large constant $C$-field
background. The non-Abelian gauge symmetry corresponds to diffeomorphisms
preserving an exact 3-form on the worldvolume, which defines a Nambu-Poisson
bracket. Various interesting geometric and algebraic properties of the theory
are discussed.
