The concept of a long-chain molecule acting as a spring in tension with the restoring force based on changes in entropy rather than energy has played a central role in the molecular theory of rubber elasticity since its inception over 50 years ago [1, 2], It is here reviewed and discussed from several different viewpoints based, in part, on insights gained from the computer simulation of atomistic models. Included are (a) kinetic interpretation of the force [3], (b) the role of excluded volume interactions in dense polymer systems [4], and (c) the extent of the utility of the entropic spring concept in nonequilib-rium situations [5].