There is a diversity of ontology languages in use, among them (mathsf{OWL}), RDF, OBO, Common Logic, and F-logic. Related languages such as UML class diagrams, entity-relationship diagrams and object role modeling provide bridges from ontology modeling to applications, e.g., in software engineering and databases. Also in model-driven engineering, there is a diversity of diagrams: UML consists of 15 different diagram types, and SysML provides further types. Finally, in software and hardware specification, a variety of formalisms are in use, like Z, VDM, first-order logic, temporal logic etc.Another diversity appears at the level of ontology, model and specification modularity and relations among ontologies, specifications, and models. There is ontology matching and alignment, module extraction, interpolation, ontologies linked by bridges, interpretation and refinement, and combination of ontologies, models and specifications.The distributed ontology, modeling and specification language (DOL) aims at providing a unified metalanguage for handling this diversity. In particular, DOL provides constructs for (1) ""as-is"" use of ontologies, models, and specifications (OMS) formulated in a specific ontology, modeling or specification language, (2) OMS formalized in heterogeneous logics, (3) modular OMS, (4) mappings between OMS, and (5) networks of OMS. This chapter sketches the design of the DOL language. DOL has been submitted as a proposal within the OntoIOp (ontology, model, specification integration and interoperability) standardisation activity of the object management Group (OMG).