This work explores the monotonic and cyclic behaviors of filled, natural rubber. Results of stress-strain experiments conducted under stress states of simple, planar, and equibiaxial tension are presented. The ability of hyperelastic models to capture the observed response, as well as recent developments in constitutive modeling of filled rubber such as the consequences of the Mullins effect, are discussed. Monotonic and cyclic multiaxial experiments were also conducted using a short, thin-walled, cylindrical specimen subjected to a wide range of combined axial and twist displacements. Experiments included pure axial tension, pure torsion, combined loading in which the axial and torsion displacements varied proportionally, and combined loading in which the axial and torsion displacements varied non-proportionally (phase between axial and torsion channels of ϕ=0 deg, 90 deg, 180 deg). Results from these tests are presented and discussed, including evolution of stress-strain behavior with load cycles, and the effects of a short period of initial overloading on the subsequent evolution of the stress-strain response.