Anxiety is an emotion which is characterized by an unpleasant state of inner turmoil and includes feelings of dread over anticipated events. Anxiety is different than fear in that the former is defined as the anticipation of a future threat whereas the latter is defined as the emotional response to a real threat. It is often accompanied by nervous behavior such as pacing back and forth, somatic complaints, and rumination.

Anxiety is a feeling of uneasiness and worry, usually generalized and unfocused as an overreaction to a situation that is only subjectively seen as menacing. It is often accompanied by muscular tension, restlessness, fatigue, inability to catch one's breath, tightness in the abdominal region, nausea, and problems in concentration. Anxiety is closely related to fear, which is a response to a real or perceived immediate threat (fight or flight response); anxiety involves the expectation of future threat including dread. People facing anxiety may withdraw from situations which have provoked anxiety in the past.

The emotion of anxiety can persist beyond the developmentally appropriate time-periods in response to specific events, and thus turning into one of the multiple anxiety disorders (e.g. generalized anxiety disorder, panic disorder). The difference between anxiety disorder (as mental disorder) and anxiety (as normal emotion), is that people with an anxiety disorder experience anxiety most of the days during approximately 6 months, or even during shorter time-periods in children. Anxiety disorders are among the most persistent mental problems and often last decades. Besides, strong percepts of anxiety exist within other mental disorders, e.g. obsessive-compulsive disorder, post-traumatic stress disorder.