  The Fierz-Pauli (FP) free field theory for massive spin 2 particles can be
extended, in a spacetime of (1+2) dimensions (3D), to a generally covariant
parity-preserving interacting field theory, in at least two ways. One is "new
massive gravity" (NMG), with an action that involves curvature-squared terms.
Another is 3D "bigravity", which involves non-linear couplings of the FP tensor
field to 3D Einstein-Hilbert gravity. We review the proof of the linearized
equivalence of both "massive 3D gravity" theories to FP theory, and we comment
on their similarities and differences.
