  We use the hamiltonian formalism to study the asymptotic structure of 3
dimensional gravity with a negative cosmological constant. We start by defining
very general fall-off conditions for the canonical variables and study the
implied poisson structure of the boundary gravitons. From the allowed
differentiable gauge transformations, we can extract all the possible boundary
conditions on the lagrange multipliers and the associated boundary
hamiltonians. In the last section, we use this general framework to describe
some of the previoussly known boundary conditions.
