Flexibility is a personality trait that describes the extent to which a person can cope with changes in circumstances and think about problems and tasks in novel, creative ways. This trait comes into play when stressors or unexpected events occur, requiring that a person change their stance, outlook, or commitment.

Flexibility, or psychological flexibility, as it is sometimes called, is the ability to adapt to situational demands, balance life demands, and commit to behaviors.

Flexible personality should not be confused with cognitive flexibility, which is the ability to switch between two concepts, and to simultaneously think about multiple concepts. Researchers of cognitive flexibility describe it as the ability to switch one's thinking and attention between tasks.

Due to the different facets of the definition of psychological flexibility, it is difficult to measure. There are multiple questionnaires that attempt to do so.

The Acceptance and Action Questionnaire (AAQ) was designed to measure experiential avoidance. This test found that higher levels of avoidance are linked to higher levels of general psychopathology, depression, anxiety, fears, and a lower quality of life. AAQ also measures avoidant coping and self-deceptive positivity. It was later decided that the AAQ actually measured psychological flexibility, not experiential avoidance. It was used until the AAQ-II was created.

The AAQ-II was developed in order to improve upon the faults of the AAQ, which included scale brevity, item wording, and item selection procedures that caused insufficient alpha levels to be obtained in measurements. AAQ-II scores predict many outcomes, including mental health and work absence rates. AAQ-II also was more psychometrically consistent than the original AAQ.

Laboratory measures of flexibility are consistent with how flexible people are in their actual lives. The validity of the AAQ has again been brought into question, primarily by inconsistent results. Studies have shown that both versions of the AAQ appear to measure the same thing, which is neuroticism/negative affect rather than experiential avoidance.

Research shows that parenting psychological flexibility may influence the relationship between parent distress and child distress. When parents are psychologically inflexible they cause more stress in their families.