Ontology design patterns are a promising approach for ontology engineering. In this chapter, we introduce the notion of Ontology Pattern Language (OPL) as a way to organize domain-related ontology patterns. This chapter is organized as follows: Section 7.1 presents the motivation for organizing Domain-Related Ontology Patterns (DROPs) as OPLs. Section 7.2 discusses what an OPL is, and how OPLs are represented, showing an example of an OPL for the software process domain, based on ISO Standards (ISP-OPL). Section 7.3 discusses how to build OPLs from core ontologies, taking ISP-OPL as an example. Section 7.4 discusses how an OPL can be used for building a domain ontology. An example applying ISP-OPL for building a domain ontology about the Stakeholder Requirements Definition Process is presented. Section 7.5 presents an overview of existing OPLs. Finally, Section 7.6 presents our final remarks.