NICS Lab is in charge of organizing the third edition of ISARCS, a symposium on architecting critical systems. Information about previous editions of this symposium can be found at http://www.isarcs.org/isarcs2011/, and at http://www.isarcs.org/isarcs2010/. ISARCS is framed within CompArch (http://www.comparch-events.org/), a federated conference series related to Component-Based Software Engineering and Software Architecture. Submissions of interest from both industry and academia, include, but are not limited to, the following main areas: – New paradigm for designing evolving critical systems: extensible architectural description languages; architectural styles; architectural patterns; architectural support for evolution; integrators (wrappers) for dependability; model-driven development; component based development; aspects oriented development; assurance based development; – Testing and analysis of evolving systems: testing; simulation; inspection techniques; type checking; run-time checks; model-checking; theorem proving; fault injection – Architecting fault-tolerant and evolvable critical systems: tolerating architectural mismatches; redundancy and diversity; survivability; error confinement; monitoring; exception handling; self-healing – Combined approaches for architecting evolving and critical systems: integrated processes; combination of methods; interplay of techniques; integration of analysis techniques; the integration of tools; – Relevant domains with critical systems: critical infrastructures; embedded systems; mobile and ubiquitous systems; automotive systems; avionic systems; e-commerce; e-business; e-government; – Industrial needs: reports about industrial case studies, challenges, problems and solutions The symposium will be held in Bertinoro, Italy, from 26th to 28th of June.