This chapter describes a GridService demonstrator built around the Unicore Grid environment, its architectural design and implementation [1]. It then examines some lessons learned from the process of developing an implementation of a family of GridServices that conforms to the Open Grid Services Architecture (OGSA) [2] and the Grid Service Specification [3]. The goals of this project were two fold. Primarily, it is only through implementation that complexities such as those that arise in OGSA can