This book constitutes the refereed proceedings of the 9th International Colloquium on Theoretical Aspects of Computing, ICTAC 2012 held in Bangalore, India, in September 2012. The 16 revised full papers presented together with the abstracts of three keynote talks were carefully reviewed and selected from 73 submissions. The papers cover various topics related to both theoretical aspects of computing and the exploitation of theory through methods and tools for system development.