This monograph is an updated and extended edition of Strength and Fracture of Polymer Films, which was published in Russian in 1999. It presents the results of long-term theoretical and experimental studies of brittle and quasi-brittle fracture of solid polymers. The principal results of a comprehensive and detailed investigation of the statistical features of fracture of polymers and other solids under the conditions of separate and complex action various factors (temperature, mechanical stresses, surface-active media, UV irradiation, gamma-irradiation, chemical admixtures, thermal modification, orientational drawing, etc.) are given. One of the most interesting and key results of this study concerns the finding of the two principal strength states: low-strength state (bulk samples) and high-strength state (thin films and fibers) as well as establishing a detailed distinction between the modes of their fracture. This monograph will be of interest to anyone working in the field of polymer films and fibers.