This paper by S. Deser, R. Jackiw, and S. Templeton explores three-dimensional Yang-Mills and gravity theories augmented by gauge-invariant mass terms. These topologically nontrivial additions significantly alter the particle content of the models, leading to the quantization of a dimensionless mass-coupling-constant ratio. The vector field excitations become massive with spin 1, and the mass provides an infrared cutoff. Gravitation acquires mass, mediates finite-range interactions, and has spin 2, despite the third derivative order of its mass term. The non-Abelian mass term also has nontrivial homotopy properties, which lead to the quantization of a dimensionless combination of mass and coupling constant. The authors analyze the linearized actions and show that all particles are massive with causal propagation. They also discuss the quantization of the models, the ultraviolet behavior of gravity and supergravity, and the relation of these models to four-dimensional theory. The paper concludes with a discussion of the external-source problem and the potential for constructing supergravity.This paper by S. Deser, R. Jackiw, and S. Templeton explores three-dimensional Yang-Mills and gravity theories augmented by gauge-invariant mass terms. These topologically nontrivial additions significantly alter the particle content of the models, leading to the quantization of a dimensionless mass-coupling-constant ratio. The vector field excitations become massive with spin 1, and the mass provides an infrared cutoff. Gravitation acquires mass, mediates finite-range interactions, and has spin 2, despite the third derivative order of its mass term. The non-Abelian mass term also has nontrivial homotopy properties, which lead to the quantization of a dimensionless combination of mass and coupling constant. The authors analyze the linearized actions and show that all particles are massive with causal propagation. They also discuss the quantization of the models, the ultraviolet behavior of gravity and supergravity, and the relation of these models to four-dimensional theory. The paper concludes with a discussion of the external-source problem and the potential for constructing supergravity.