Earth System Modelling strongly relies on a wide data base: Data serve as input in models and the model results have to been compared with other models or observational data. Unfortunately, the existing data are distributed over many archives and databases and vary highly in quality, available description (metadata), and accessibility. This encumbers collaborative work of scientists and makes routine workflows often tedious.The implemented infrastructure provides tools for effective data discovery and data transfer. A central catalogue of discovery metadata enables the user to seek after data in all connected data archives. The user can specify regional and time constraints, variable names and experiment labels for his data query. The provider specific implementation of the data access as well as of the data preparation is hidden behind a common WSDL defined web service interface. Thus the user has transparent and uniform access to all data archives within C3Grid.