The internet as a communication medium has proven to be an effective alternative to in-person therapy in recent years. This manual provides a practice-oriented presentation of cognitive-behavioral therapy methods as well as transdiagnostic approaches in an internet-based setting. The aim of the book is to demonstrate the applicability of online therapy and counseling. This is intended to facilitate a practical use of the internet as a therapeutic field. The book first offers a current overview of the range of application areas of new communication media in psychological care, as well as the effectiveness of internet-based therapy and counseling approaches. It describes how internet-based diagnostics and exploration can be conducted. Subsequently, it details in a practical manner how cognitive-behavioral therapy methods can be applied.