The most common function of NSSI is emotion regulation. However, the differentiation between adaptive and maladaptive strategies is overly simplistic. More recent approaches focus on psychological flexibility, which is seen as an important determinant of mental health and well-being. More specifically, the present project will investigate behavioral, cognitive, and emotion regulation flexibility as well as its associations in youth with NSSI. Behavioral flexibility refers to the adaptive change of behavior in response to changing environmental contengenies. Cognitive flexibility, which refers to the ability to adapt responses/strategies based on environmental feedback. Emotion regulation flexibility refers according to Aldao et al. (2015) as “the degree of covariation between variation in the use of one or more emotional regulation strategies across a number of environments, while the environment might consist of external events or appraisals of emotional reactions to such events.” So, there are two core elements to emotional flexibility, sensitivity to situational demands and the ability to regulate emotions accordingly. Details will be discussed.