The increasing number of Web services over the Web makes the requester to use tools to search for suitable Web services available throughout the globe. UDDI is the first step towards meeting these demands. However the requester’s demand may include not only functional aspects of Web services but also non-functional aspects like Quality of Service (QoS). There is a need to select the most suitable (qualitatively optimal) Web service based on the requester’s QoS requirements and preferences. In this paper we explore the different types of requester’s QoS requirements (demands) with illustrations. We propose the QoS broker based architecture for dynamic Web service selection which facilitates the requester to specify his/her QoS requirements along with functional requirements. The paper presents the Web service selection mechanism which selects the best (most suitable) Web service based on the requester’s functional and quality requirements.