We describe the Dirichlet space of M-harmonic functions, i.e. functions annihilated by the invariant Laplacian on the unit ball of the complex n-space, as the limit of the analytic continuation (in the spirit of Rossi and Vergne) of the corresponding weighted Bergman spaces. Characterizations in terms of tangential derivatives are given, and the associated inner product is shown to be Moebius invariant. The pluriharmonic and harmonic cases are also briefly treated.