The following technical report is available from http://aib.informatik.rwth-aachen.de: The MeDUSA Reference Manual, Second Edition Alexander Nyßen, Horst Lichter AIB 2008-07 MeDUSA (Method for UML2-based Construction of Embedded & Real-Time Software) is a model-based software construction method targeting the domain of small embedded & real-time software. MeDUSA was developed by the Research Group Software Construction of the RWTH Aachen University in close cooperation with the German ABB Corporate Research Centre. It incorporates various practical experiences gained during the industrial development of embedded software in ABB Business Unit Instrumentation. Being Use Case-driven, MeDUSA systematically covers the software construction lifecycle phase from the early requirements up to implementation. Models are successively developed and employed throughout all activities. By enforcing a class-based rather than an object-oriented design, a smooth transition of the resulting design model towards an implementation in a procedural programming language is facilitated. This is essential, as procedural programming languages as the C language are still state-of-the-art in the domain of small embedded & real-time software.