Invited Speakers -- A Rewriting Logic Sampler -- Codes and Length-Increasing Transitive Binary Relations -- Languages and Process Calculi for Network Aware Programming – Short Summary - -- Stochastic Analysis of Graph Transformation Systems: A Case Study in P2P Networks -- Component-Based Software Engineering -- Formal Languages -- Outfix-Free Regular Languages and Prime Outfix-Free Decomposition -- Solving First Order Formulae of Pseudo-Regular Theory -- Splicing Array Grammar Systems -- Computer Science Logics -- Compositionality of Fixpoint Logic with Chop -- An SLD-Resolution Calculus for Basic Serial Multimodal Logics -- Upside-Down Transformation in SOL/Connection Tableaux and Its Application -- Program Construction -- On the Stability Semantics of Combinational Programs -- Generating C Code from LOGS Specifications -- Formalizing the Debugging Process in Haskell -- Finding Resource Bounds in the Presence of Explicit Deallocation -- Real-Time Systems -- The Timer Cascade: Functional Modelling and Real Time Calculi -- A Robust Interpretation of Duration Calculus -- Symbolic Model Checking of Finite Precision Timed Automata -- Concurrency and Refinement -- Covarieties of Coalgebras: Comonads and Coequations -- Linking Theories of Concurrency -- On Cool Congruence Formats for Weak Bisimulations -- Externalized and Internalized Notions of Behavioral Refinement -- Software Security -- Information Flow Is Linear Refinement of Constancy -- On Typing Information Flow -- Representation and Reasoning on RBAC: A Description Logic Approach -- Revisiting Failure Detection and Consensus in Omission Failure Environments -- Quantitative Logics -- Congruences and Bisimulations for Continuous-Time Stochastic Logic -- A Logic for Quantum Circuits and Protocols -- Quantitative Temporal Logic Mechanized in HOL -- Weak Stochastic Bisimulation for Non-markovian Processes -- Object-Orientation and Component Systems -- On Refinement of Software Architectures -- POST: A Case Study for an Incremental Development in rCOS -- Implementing Application-Specific Object-Oriented Theories in HOL -- Constructing Open Systems via Consistent Components -- Model-Checking and Algorithms -- A Sub-quadratic Algorithm for Conjunctive and Disjunctive Boolean Equation Systems -- Using Fairness Constraints in Process-Algebraic Verification -- Maximum Marking Problems with Accumulative Weight Functions -- Applied Logics and Computing Theory -- Toward an Abstract Computer Virology -- On Superposition-Based Satisfiability Procedures and Their Combination -- Tutorials at ICTAC 2005 -- A Summary of the Tutorials at ICTAC 2005.This volume contains the proceedings of ICTAC 2005, the second ICTAC, International Colloquium on Theoretical Aspects of Computing. ICTAC 2005 took place in Hanoi, Vietnam, October 17–21, 2005. ICTAC was founded by the International Institute for Software Technology of the United Nations University (UNU-IIST) to serve as a forum for practiti- ers, lecturers and researchers from academia, industry and government who are interested in theoretical aspects of computing and rigorous approaches to so- ware engineering. The colloquium is aimed particularly, but not exclusively, at participants from developing countries. We believe that this will help developing countries to strengthen their research, teaching and development in computer science and engineering, improve the links between developing countries and developed countries, and establish collaboration in research and education. By providingavenueforthediscussionofcommonproblemsandtheirsolutions,and for the exchangeof experiencesand ideas,this colloquiumsupportsresearchand development in computer science and software technology. ICTAC is attracting more and more attention from more and more countries.