This document addresses interoperability in a broad sense, in the context of data, in particular for materials and manufacturing. It is meant for developers (at domain level) of ontologies and platforms, tools or components that use them. To set the stage and give an overview of the various facets of the topic, the document collects existing definitions and classifications of interoperability (its types, layers, levels) and points to recommendations from various entities and communities. Next, it provides an analysis of a set of interoperability scenarios, proposes a classification of broad interoperability requirements and components to address them. Finally, it summarizes advice from OntoCommons on interoperability issues.