Treatment integrity refers to the degree to which an intervention is implemented as intended. This book examines the adequacy of treatment integrity procedures in randomized controlled trials of psychosocial interventions and evaluates the associated factors. Results indicate that investigations that systematically implement treatment integrity procedures are virtually lacking in the literature. Skill-building treatments (e.g., cognitive-behavioral) as compared to non skill-building interventions (e.g., psychodynamic) were implemented with higher attention to integrity. Treatment integrity was addressed to a greater degree when interventions were evaluated using a treatment manual. Implications of the obtained results for psychotherapy research and practice, recommendations for improving how integrity is addressed, as well as guidelines on treatment integrity procedures are discussed. Further, this book includes a measure for assessing the adequacy of treatment integrity procedures and a rater manual.