A combination of DSC, SAXS, WAXD, H-1 time-domain, and frequency domain NMR measurements was used for determining the amount of rigid/crystallinity, semirigid, and soft fractions of iPP. Changes in the rigid, semirigid, and soft fractions of isotactic polypropylene (iPP) were investigated as a function of temperature, annealing time, and annealing temperature. The most probable iPP morphology was established by TEM and by comparing H-1 spin-diffusion data with data from multidimensional solutions of the spin-diffusion equations. Proton NMR spin-diffusion method, which employs double-quantum (DQ) and Goldman-Shen dipolar filters, was used in order to provide the domain thickness in iPP. The temperature dependence of spin diffusivities was taken into account, and a semiquantitative theory is presented for this dependence in the case of amorphous domains. A combination of H-1 spin-diffusion NMR and SAXS was used to estimate the lamellar thicknesses for nonannealed and annealed iPP samples. Annealing at temperatures above 110 degrees C causes increases in the lamellar thickness and the crystallinity and a decrease in the chain mobility of rigid and semirigid fractions. The above quantities and the chain dynamics are reported for three annealing temperatures, 134, 143, and 153 degrees C, and an annealing time in the range of 15 min to 30 h. It is shown that the crystalline domains thickening during annealing of iPP can be described by a model based on irreversible thermodynamics. A phenomenological correlation is established between H-1 transverse magnetization relaxation rate of the rigid fraction of iPP and the annealing temperatures.