Ontologies are considered a key technology enabling semantic interoperability and integration of data and processes. We are now entering a phase of knowledge system development, in which ontologies are produced in larger numbers and exhibit greater complexity. Also we have witnessed an increasing need for technologies that enable the reuse of existing (Semantic) Web resources from within the ontology engineering environment itself. In the NeOn project we aim at advancing the state of the art in using ontologies for large-scale semantic applications. This is realized by providing an infrastructure for networked ontology management and engineering capable of suiting the community’s needs [1]. The heart of this infrastructure is the NeOn Toolkit for engineering contextualized networked ontologies and semantic applications. The shift from closed semantic applications, characterized by a monolithic corporate ontology, to open semantic applications, characterized by networks of ontologies, implies that a number of other aspects like dealing with context, collaboration or data and web integration become crucial. The NeOn Toolkit was built with the web-centric elements of semantic technologies in mind: much like Web 2.0 environments emphasize distributed content production, the NeOn Toolkit features methods and tools for managing knowledge that is distributed, heterogeneous, contextualized, and developed collaboratively.