The international research community involved in the GMES, INSPIRE, and GEOSS initiatives is actively pursuing the specification of information and service oriented solutions for geospatial data interoperability. A prominent interoperability issue pertains to discovery services. From an information technology point of view, the challenge is to implement interoperable discovery services for data and processing resources that are collected and managed using multidisciplinary standards and tools. We have designed and experimented a new, improved model and technology for the discovery of geospatial resources: an advanced catalog service featuring additional functionalities like mediation and asynchronous distribution. Besides, the described solution addresses another well-recognized issue: the integration of discovery and access services for complex resources-such as EO datasets.