SeaDataNet is a pan-European distributed marine data infrastructure for the management, exchange and re-use of marine and oceanographic data sets and collections. A major objective and challenge in SeaDataNet is to promote discoverability of these data resources in a consistent and comprehensive manner. This is achieved through the SeaDataNet metadata services a set of directories, with associated user interfaces and web services, each governed by a SeaDataNet partner and content provided through national SeaDataNet collating nodes. The European Directory of Ocean-Observing Systems (EDIOS) is the SeaDataNet catalogue promoting discoverability of, and access to, ocean measuring and monitoring systems operated by European countries. EDIOS is an initiative of the European Global Ocean Observing System (EuroGOOS) and helps to maintain visibility of continuously available data sets for operational modelling purposes and supports implementation of the European Unions Marine Strategy Framework Directive (MSFD). EDIOS presents users with three main tiers of information: monitoring i) programmes, ii) platforms and iii) series/stations. The catalogue utilises a metadata format based upon the ISO 19115 content model. The EDIOS Schema and XML coding are supported by URLs and URNs to the SeaDataNet Common Vocabularies.For communities who need information about marine monitoring initiatives operated by European countriesMore than 110 data providers (linked to more than 600 data originators) and several thousands of data users.