The goal of Digital Earth (www.digitalearth.gov) is to create a virtual representation of our planet that enables a person to explore and interact with the vast amounts of natural and cultural informationgathered about the Earth. The challenge is enormous, and a critical first step is interoperability among the servers, viewers, catalogs and middleware services in such a distributed computing network. As part of its contribution to the public/private/academic Digital Earth (DE) partnership, a NASA Testbed is implementing the OpenGIS Consortium (OGC) Web Map Server Interface Specification on several data servers and viewer clients, and is building an OGC Catalog Services prototype implementation. Viewers will include a web-based client, an immersive 3D workbench client, and a wall-sized museum display client. Servers will provide global, regional and local environmentalinformation from satellites, climate models and ground stations. This paper describes the Web Mapping spec and the com...