A theory of crack healing in polymers is presented in terms of the stages of crack healing, namely, (a) surface rearrangement, (b) surface approach, (c) wetting, (d) diffusion, and (e) randomization. The recovery ratioRof mechanical properties with time was determined as a convolution product,R=Rh(t)*&fgr;(t), whereRh(t) is an intrinsic healing function, and &fgr;(t) is a wetting distribution function for the crack interface or plane in the material. The reptation model of a chain in a tube was used to describe self‐diffusion of interpenetrating random coil chains which formed a basis forRh(t). Applications of the theory are described, including crack healing in amorphous polymers and melt processing of polymer resins by injection or compression molding. Relations are developed for fracture stress &sgr;, strain &egr;, and energyEas a function of timet, temperatureT, pressureP, and molecular weightM. Results include (i) during healing or processing att<t∞, &sgr;,&egr;∼t1/4,E∼t1/2; (ii) at constantt<t∞, &sgr;,&egr;∼M−1/4,E∼M−1/2; (iii) in the fully interpenetrated healed state att=t∞, &sgr;,&egr;∼M1/2,E∼M; (iv) the time to achieve complete healing,t∞∼M3, ∼exp P, ∼exp 1/T. Chain fracture, creep, and stress relaxation are also discussed. New concepts for strength predictions are introduced.