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The role of fracture mechanics in ASME Section XI applications comes in the form of evaluation of indications or flaws detected during inservice inspection of nuclear components. The need to include the influence of significant plastic deformation, which may accompany crack initiation and the subsequent stable growth, has been the main driving force for the development of the field of elastic-plastic fracture mechanics (EPFM). This chapter traces the history of development of the EPFM from the 1960s and reviews the EPFM applications in Section XI Code. It discusses the three approaches considered in the application of EPFM in flaw evaluations: J-integral tearing modulus-based approach or J-T methodology, deformation plasticity failure assessment diagram (DPFAD) methodology, and R-6 methodology. The engineering estimation of the applied J integral is described, followed by a discussion on the application of the J-T approach in the evaluation of flaws in austenitic stainless steel piping and ASME Class 1 ferritic piping. The chapter describes the application of EPFM to reactor pressure vessel evaluation in three distinct ways: upper-shelf energy evaluation, Section XI flaw evaluation approach, and a probabilistic approach. It also explains the application of the Master Fracture Toughness Curve method to evaluate pressure vessel steels based on EPFM. The current activity within the ASME Section XI Code Groups related to the potential revision of ASME Code Case N-830 is finally summarized.