Interoperability between heterogeneous, distributed services, is one of the key features of the Virtual Observatory. CDS develops widely used interoperability tools, VizieR and Aladin. Tabular data, catalogues, published tables, surveys, and lists of observations in archives, are federated in VizieR, with active links to data, images, spectra and time series, for instance with links to archives such as HST, CFHT and ISO. Aladin gives access to images and to tabular data. In addition to data held at CDS, databases such as NED and SIMBAD, and links from VizieR, additional resources can be described through the GLU (Générateur de Liens Uniformes). A set of exchange standards have been discussed by consortia of potential users: ASU - Astronomical Server URL, to generate queries; astrores, XML description of catalogues and query results. astrores is put in action in HEASARC Browse and IRSA OASIS. In addition, an XML description of SIMBAD is in preparation, and an XML frame for image data sets, taking into the FITS expertise, is discussed. On the other hand, the UCDs (Uniform Column Descriptor), developed in the frame of the ESO/CDS Data Mining project, are prototypes of metadata categorizing catalogue contents. They will be used for data mining purposes, and open the way for automated conversion of parameters. A prototype of interoperability between representative ground-based and space archives (ESO, ESA, UK archives from AstroGRID, Terapix, Jodrell Bank), based on VizieR and Aladin, is being implemented in the frame of the Astronomical Virtual Observatory project, recently selected by the European Commission.