There seems to be a general consensus on the crucial role metadata can play for enhancing the functionalities of scientific workflows systems, e.g., workflow and service discovery, composition and provenance browsing, among others. However, in most cases their management is under-specified, if not left unaddressed at all. A step in this direction, the main contribution of the work presented in this paper is an overview of metadata and their management in the Taverna workflow system. In Taverna, we consider metadata to be a first class citizen in the system, in the sense that we fully cover their life cycle from their creation, through their use and curation until their eventual removal. We present the main steps of this cycle and present the models used for metadata specification. In doing so, we distinguish two classes of metadata: metadata that describe workflow related entities, such as services, workflows and sub- workflows, and metadata that describe workflow executions, also known as workflow provenance.