This book constitutes the refereed proceedings of the 27th International Conference on the Foundations of Software Technology and Theoretical Computer Science, FSTTCS 2007, held in New Delhi, India, in December 2007.The 40 revised full papers presented together with 5 invited papers were carefully reviewed and selected from 135 submissions. The papers provide original research results in fundamental aspects of computer science as well as reports from the frontline of software technology and theoretical computer science. 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.