The statistical and phenomenological theories of rubber elasticity are reviewed briefly. Combining recent concepts proposed by Yeoh and Gent, a new theory is proposed. The proposed constitutive model for rubber vulcanizates invokes two mechanisms; one influences behavior at small strains while the other dominates behavior at large strains. Network flaws, such as entanglements, are suspected to be responsible for the first mechanism. Finite extensibility of network chains is identified as the cause of the second. Thus, macroscopic behavior is directly linked to molecular concepts. The proposed theory allows prediction of the stress-strain behavior of a family of four rubber vulcanizates in different modes of deformation (simple extension, compression, and simple shear) from regression analysis of tensile data alone from just one member.