This presentation concerns pragmatic approaches on achieving interoperability in digital libraries and repositories based on relevant experiences of the authors in real-life, large scale, successful use cases such as: (a) the establishment – within the EuropeanaLocal project – of a national aggregator, harvesting digital content (more than 170000 records) from various repositories across the country to incorporate it into Europeana, the single portal / gateway to distributed European cultural heritage resources developed as an initiative of the European Commission, (b) the development and operation of openarchives.gr, a single, unified search engine over Greek digital libraries and repositories that currently indexes metadata from 39 systems (more than 340000 records) and (c) the inclusion of content (roughly 40000 items) from disparate data sources to Pandektis, a thematic repository of cultural heritage and humanities material and Helios – the institutional repository of the National Hellenic Research Foundation.