Solid-state C-13, F-19, and N-15 magic angle spinning NMR studies of Form I of atorvastatin calcium are reported, including chemical shift tensors of all resolvable carbon sites and fluorine sites. The complete C-13 and F-19 chemical shift assignments are given based on an extensive analysis of C-13-H-1 HETCOR and C-13-F-19 HETCOR results. The solid-state NMR data indicate that the asymmetric unit of this material contains two atorvastatin molecules. A possible structure of Form I of atorvastatin calcium (ATC-I), derived from solid-state NMR data and density functional theory calculations of various structures, is proposed for this important active pharmaceutical ingredient (API).