This manuscript provides a user's guide for the human reliability analysis (HRA) method known as "A Technique for Human Event Analysis" (ATHEANA), which the U.S. Nuclear Regulatory Commission (NRC) documented in NUREG-1624, Rev. 1, dated May 2000. As the first publication of its kind, this user's guide describes both the quantitative and qualitative ATHEANA analysis approaches, fully describing the revised quantification approach and presenting a...