The fine‐scale structure that exists in polytetrafluoroethylene fibers produced by different methods was investigated by electron microscopy and electron diffraction. These fibers were formed by mechanically abrading the surface and by fracture of compacted granular grade PTFE, and by stripping the fibers from the surface of Teflon‐coated aluminum foil. Bright‐field electron microscope observations indicate that the fibers are composed of microfibers or fibrils with a nearly uniform diameter of 450 Å. These fibrils are composed of platelet‐like units 60 Å thick, oriented normal to the fiber axis, and are organized into blocks on the order of 475 Å in length. Electron diffraction from unshadowed individual fibers indicates that the crystal size must be fairly large, with few defects. These observations are well supported by the dark‐field micrographs of the fibers. The dark‐field photographs show crystalline regions along these fibrisl, which appear to be multiples of the fundamental 450‐Å fibrill diameter, with a range in lnegth of 160–7000 Å. Additional observations of the fibrils indicate that these molecular packets can slide past one another, either individually or in groups. Examples of slip or shear, bowing, rotation, and kinking of the platelet‐like structures have been observed.