The majority of aviation accidents are attributable to human error. Moreover, as machines (or mechanical systems) have become more reliable over the past decades, human error has outpaced machine problems as a major contributing factor in aviation accidents. It is therefore important to address human error for the improvement of aviation safety. Human error typically occurs as a result of poor interactions among operators, machines, and environment, and it is often influenced by group dynamics and organizational factors. This presentation introduces 1) what human error is, 2) the relationship between human error and aviation safety viewed from individual, group, and organizational perspectives, and 3) solutions to reduce human error.