Quality of Service (QoS) support in web services plays a great role in their success. Composing web services to provide new functionalities is gaining more and more momentum while the number of available web services proliferates and the need for composite web services increases. In this paper, we develop a novel architecture, called CompQoS, for QoS composition, verification, and monitoring of composed web services. The CompQoS architecture supports also the composition of differentiated classes of QoS. A set of QoS composition patterns is applied to achieve an analytical verification of composed QoS. These patterns are derived from the BPEL process and can be the logic of composition, the way of invocation of web services partners, and the composition flow logic. An agent-based monitoring approach has been used to monitor, validate, and enforce the aggregated QoS of a composed web service. Finally, the architecture is demonstrated through a case study for verifying and monitoring the QoS of a composed teleconferencing web services in a 3G network.