Present research project aims to evaluate a transdiagnostic intervention protocol (Eureka; training emotion regulation in adolescents) for adolescents 10-14 years, diagnosed with internalizing or externalizing problems and seeking help in inpatient or outpatient clinical settings The transdiagnostic protocol is innovative as it incorporates the training of different well-evaluated emotion regulation strategies and skills in a strict structured sequens Based on series of single case studies, effects are expected on degree of psychopathology as primary outcome Next, weekly effects on stress, emotion regulation and affect will also be assessed through self-report and further validated with a psychophysiology measure Furthermore, aiming to increase homework compliance, we will develop and evaluate the effect of providing homework through eHealth channels, resulting in  a new EuREKA format In order to fulfill this aim, the project will comprise 3 WP's scrutinizing the outcome of the EuREKA training using single-case methodology, preceded by a systematic review on blended care youth mental health interventions whereby a final study will evaluate the assumed important role of the first emotion regulation skill of the structured sequens of the training: emotional awareness The project will set the stage for developing a groundbreaking RCT