The objectives of the CATI project (Charging and Accounting Technology for the Internet) include the design, implementation, and evaluation of charging and accounting mechanisms for Internet services and Virtual Private Networks (VPN). They include the enabling technology support for open, Internet-based Electronic Commerce platforms in terms of usage-based transport service charging as well as high-quality Internet transport services and its advanced and flexible configurations for VPNs. In addition, security-relevant and trust-related issues in charging, accounting, and billing processes are investigated. Important application scenarios, such as an Internet telephony application as well as an Electronic Commerce shopping network, demonstrate the applicability and efficiency of the developed approaches. This work is complemented by an appropriate cost model for Internet communication services, including investigations of suitable usage-sensitive pricing models.