Psychotherapy describes a central field within the German health care system for adults as well as for children and adolescents. In the federal republic of Germany about 10% of children and adolescents are known to suffer from mental disorders. The quality of life and family life of these children are thereby often extremely reduced. Over the last years, a large and growing body of research on effectiveness of treatments for psychiatric disorders in childhood and adolescence has been published. The increase in the number of studies in general makes it difficult to get an overview on the current status of research. The aim of this work is to present an up-to-date summary on efficacy of psychological and psychiatric interventions in childhood and adolescence, published between 2000 and 2007. Article 1 and 2 are based on a systematic literature search of the existing meta-analyses and reviews on the four most frequent child and adolescent psychiatric disorders: anxiety disorder, depression, ADHD, conduct disorder (CD). Presentation of the results follows a dichotomous classification (internalizing vs. externalizing disorders), with article 1 reporting the results on anxiety disorders and depressive disorders and article 2 reporting the results on ADHD and CD. In addition to an up-to-date summary of treatment effects, an overview of open research questions is given. The majority of reviews focuses on the treatment of depressive disorders and ADHD. In view of the current situation of research the following can be stated: There is a reasonable amount of data concerning psychotherapeutic interventions for anxiety disorders as well as for CD which enable clear deductions. In contrast to this the state of research in depressive disorder is fragmentary and insufficient. For ADHD there is an evident lack of recent studies or surveys in psychological-psychosocial interventions. With regard to pharmacotherapeutic therapy ADHD is the only disorder which is profoundly underpinned with database. The pharmacological treatment of depressive disorders on the other hand has only moderate effects and the use of SSRI is currently overlaid by the security debate. For anxiety disorders and CD there are still less pharmacological studies available. While the use of SSRI in treatment of anxiety disorder is empirically supported, there is insufficient knowledge within the area of CD. In the area of combined treatment DHD shows – relatively speaking – the best results. Nevertheless for all four disorders database is still insufficient. Only for ADHD, the use of medication (stimulants) is considered to be the most efficacious treatment option available. For the remaining three disorders, psychotherapy is recommended as the most effective treatment of choice. Considering the efficacy, treatments for ADHD and anxiety disorders produce higher effect-sizes than interventions for depressive and CD (with medium effect sizes as average). Empirically supported treatment recommendations can be derived for anxiety disorders, depressive disorders, ADHD and CD. For all disorders and also in general, there are several desiderata (content and methodological aspects) to be incorporated in future research. During the past years and decades research primarily focused on efficacy studies, therefore the need for effectiveness studies was avowed. However, although controlled therapy studies at laboratory settings (efficacy studies) present evidence for the existence of efficient psychotherapeutic and pharmacotherapeutic treatment methods for most mental illnesses in children and adolescents, it is not clear how successful the psychotherapeutic and pharmaceutical treatments of outpatients are (effectiveness studies). The work presented here is intended as a first step towards addressing this deficit. We present data concerning the effectiveness of child and adolescent psychiatric therapies in an outpatient and naturalistic setting („treatment as usual“) as collected in German practices (article 3). Regarding the whole group of patients, no evidence for treatment effect is perceived. However, partitioning the group into four subgroups corresponding to four disorders we find small to moderate treatment effects for patients with ADHD and anxiety disorders. The findings of this prospective observational study are corroborated by propensity score analysis, a method whereby randomisation can be imitated, ensuring that relevant covariates are controlled. The difference between the calculation of treatment effects with and without propensity score analysis is substantial and underlines the necessity of using this method for analysing similar kinds of data. Compared to efficacy studies, the results of this investigation should be considered as remarkable. Treatment effects for the different specific disorders are comparable with results from previous studies.