This document discusses Sirius, a graphical modeling tool for defining domain-specific languages (DSLs) within the Eclipse environment. Sirius allows developers to create custom multi-view modeling workbenches for DSLs without needing expertise in GMF/EMF. It provides both a specification environment for defining DSLs and a runtime environment for end users. Sirius is an open source Eclipse project that has been used to create over 500 modeling workbenches with diagrams containing over 1.3 million elements.