This paper describes the development and use of an extensible service provider toolkit (ESP) for an Earth Science service-oriented architecture (SOA). Grid-enabled Earth Science applications and tools are beginning to use web services to integrate distributed resources and legacy applications. Unfortunately, each application requires substantial effort often repeated to implement base Grid functionality before addressing application-specific requirements. In an effort to help Earth Science application developers more rapidly develop these web services, we have created an extensible service provider toolkit. The toolkit provides the foundation to develop specialized services for Earth Science Grids, including legacy application and computational resource services. To demonstrate the functionality of ESP, we redeveloped several existing web services and illustrate ESP?s benefits, including reduced software development time and software reuse.