People have inherent strengths and weaknesses that can affect their performance. Issues such as fatigue, emotional stress, and motivation can adversely affect performance. Their performance is also influenced by factors external to the individual, such as poor equipment design, inadequate training, excessive workload, and the work environment. Most incidents in the process and related industries involve human factors, often as a key causal factor. Understanding these performance-shaping factors is essential for conducting good incident investigations. However, besides those involved in the actual incident, human factors can affect other aspects of the incident investigation process, especially when considering other stakeholders. The content of this article will raise awareness of how human factors can affect the success of the incident investigation process, and help others plan for improved investigations. (C) 2012 American Institute of Chemical Engineers Process Saf Prog, 2012