Feedback-informed therapy (FIT) represents a transtheoretical approach designed to enhance psychological treatments by integrating systematic, repeated assessments of patient outcomes into clinical decision-making. Despite the demonstrated efficacy of cognitive-behavioral therapy (CBT), a significant proportion of patients fail to benefit from treatment, emphasizing the need for tools that improve prediction and intervention for nonresponsive cases. FIT achieves this by employing routine outcome monitoring (ROM), which provides therapists with patient progress data contextualized against empirical norms to guide treatment adaptations. This book offers a comprehensive introduction to FIT, detailing its empirical support, mechanisms, and practical applications. Research indicates that FIT improves treatment outcomes, particularly for patients at risk of negative outcomes, by enabling therapists to identify and respond to emerging risks. These effects are further enhanced when combined with clinical support tools (CSTs), which provide targeted interventions for at-risk patients. The book explores the variability among feedback systems in terms of assessment frequency, content, and the format of feedback, addressing the mechanisms underlying its effectiveness, such as improved patient monitoring and the strengthening of the therapeutic alliance. Divided into three parts, the book first reviews various FIT systems and their clinical applications worldwide. The second section examines adaptations of FIT for specific challenges, such as suicidal ideation and group therapy, while the final section focuses on the technological and practical implementation of FIT in diverse settings. Through case studies, guidelines, and insights into overcoming implementation barriers, the book equips clinicians with actionable strategies for integrating FIT into practice, thereby advancing personalized and effective psychotherapeutic care.