Ontology is the explicit, formal specification of shared conceptualization in a domain. It is one of the formal ways to represent knowledge. Semantically linking across ontologies is the basic backbone to ensure interoperability between agents or services. Moreover, ontology matching becomes a central issue, when building a Semantic Web, also known as "web of data." With the development of social networking web sites and linked data, huge amount of data is published on the web, which not only imposes new technology challenges over conventional ontology matching algorithms, but also demands new techniques for automatic instance level matching to support discovery and management of different individual descriptions referring to same real world object. OIM compares different individuals within same or across heterogeneous ontologies with the goal of recognizing same real world entity. This book presents an efficient and scalable ontology instance matching approach.