GT-VMT 2013 is the twelfth workshop of a series that serves as a forum for all researchers and practitioners interested in the use of visual notations (especially graph-based), techniques and tools for the specification, modeling, validation, manipulation and verification of complex systems. The aim of the workshop is to promote engineering approaches that provide effective sound tool support for visual modeling languages, enhancing formal reasoning at the syntactic as well as semantic level (e.g., for model specification, model analysis, model transformation, and model consistency management) in different domains, such as UML, Petri Nets, Graph Transformation or Business Process/Workflow Models. This year's workshop has a special theme of the analysis of non-functional / extra-functional / quality properties like performance, realtime, safety, reliability, energy consumption. We particularly encourage submissions that focus on the definition and the evaluation of such properties using visual/graph specification techniques, ranging from underlying theory through to their utility in complex system design. As a summary, topics relevant to the scope of the workshop include (but are not restricted to) the following: visual languages definition and syntax (incl. meta-modelling, grammars and graphical parsing); static and dynamic semantics of visual languages (incl. OCL, graph constraints, simulation, animation, compilation); visual/graph-based analysis in software engineering (incl. testing, verification & validation, static & dynamic analysis techniques); visual/graph constraints (incl. definition, expressiveness, analysis techniques involving constraints); model transformations and their application in model-driven development (incl. in particular, transformations between graphical and textual formalisms); visual modeling techniques and graph transformation applied to patterns; visual modeling techniques and graph transformation applied to novel architectural paradigms (e.g. service-oriented, GRID, and P2P computing, context-aware and adaptive applications, etc.) and to domains such as engineering, biology, and medicine; case studies and novel application areas; tool support and efficient algorithms. Matthias Tichy (Chalmers Technical University and Gothenburg University, Gothenburg, Sweden) Leila Ribeiro (Univ. Federal do Rio Grande do Sul, Porto Alegre, Brazil) Dates: Saturday March 23th, 2013 and Sunday March 24th, 2013