This book constitutes the refereed proceedings of the 25th International Conference on the Foundations of Software Technology and Theoretical Computer Science, FSTTCS 2005, held in Hyderabad, India, in December 2005.

The 38 revised full papers presented together with 7 invited papers were carefully reviewed and selected from 167 submissions. A broad variety of current topics from the theory of computing are addressed, ranging from software science, programming theory, systems design and analysis, formal methods, mathematical logic, mathematical foundations, discrete mathematics, combinatorial mathematics, complexity theory, and automata theory to theoretical computer science in general.