OAIster is a union catalog of digital resources. It provides access to these digital resources by "harvesting" their descriptive metadata (records) using OAI-PMH (the Open Archives Initiative Protocol for Metadata Harvesting). The Open Archives Initiative is not the same thing as the Open Access movement.
These resources, often hidden from search engine users behind web scripts, are known as the "deep web." The owners of these resources share them with the world using OAI-PMH.
OAIster reveals these digital resources in an easy-to-use, searchable interface.