Anger is an intense emotional state involving a strong, uncomfortable and non-cooperative response to a perceived provocation, hurt, or threat.

A person experiencing anger will often experience physical effects, such as increased heart rate, elevated blood pressure, and increased levels of the stress hormones adrenaline and noradrenaline. Some view anger as an emotion that triggers part of the fight or flight response. Anger becomes the predominant feeling behaviorally, cognitively, and physiologically when a person makes the conscious choice to take action to immediately stop the threatening behavior of another outside force.

Anger can have many physical and mental consequences. The external expression of anger can be found in facial expressions, body language, physiological responses, and at times public acts of aggression. Facial expressions can range from inward angling of the eyebrows to a full frown. While most of those who experience anger explain its arousal as a result of "what has happened to them", psychologists point out that an angry person can very well be mistaken because anger causes a loss in self-monitoring capacity and objective observability.

Modern psychologists view anger as a normal, natural, and mature emotion experienced by virtually all humans at times, and as an emotion that has functional value for individual survival and mutual cooperation. However, uncontrolled anger can negatively affect personal or social well-being and may produce deleterious health effects and negatively impact those around them. While many philosophers and writers have warned against the spontaneous and uncontrolled fits of anger, there has been disagreement over the intrinsic value of anger. The issue of dealing with anger has been written about since the times of the earliest philosophers, but modern psychologists, in contrast to earlier writers, have also pointed out the possible ill effects of suppressing anger on one's well-being and interpersonal relationships.

Three types of anger are recognized by psychologists:

Anger can potentially mobilize psychological resources and boost determination toward correction of wrong behaviors, promotion of social justice, communication of negative sentiment, and redress of grievances. It can also facilitate patience. In contrast, anger can be destructive when it does not find its appropriate outlet in expression. Anger, in its strong form, impairs one's ability to process information^{[citation needed]} and to exert cognitive control over one's behavior. An angry person may lose their objectivity, empathy, prudence or thoughtfulness and may cause harm to themselves or others. There is a sharp distinction between anger and aggression (verbal or physical, direct or indirect) even though they mutually influence each other. While anger can activate aggression or increase its probability or intensity, it is neither a necessary nor a sufficient condition for aggression.

Extension of the stimuli of the fighting reactions: At the beginning of life, the human infant struggles indiscriminately against any restraining force, whether it be another human being or a blanket which confines their movements. There is no inherited susceptibility to social stimuli as distinct from other stimulation, in anger. At a later date the child learns that certain actions, such as striking, scolding, and screaming, are effective toward persons, but not toward things. In adults, though the infantile response is still sometimes seen, the fighting reaction becomes fairly well limited to stimuli whose hurting or restraining influence can be thrown off by physical violence.

Brain regions which are activated when recognizing threat or provocation, and facilitate autonomic arousal and interoception and activate the stress response, are the salience network (dorsal anterior cingulate cortex and anterior insula cortex) and subcortical area (the thalamus, the amygdala, and the brain stem).