Welcome to the third annualWorkshopon Algorithms and Computation (WAL- COM 2009). The workshop provided a forum for researchers working in al- rithms and theory of computation from all over the world. This volume contains the papers presented at WALCOM 2009 held during February 18-20, 2009 at the Indian Statistical Institute, Kolkata, India. The scienti?c program of WALCOM 2009 included 30 contributed papers selected throughaveryhighqualityrefereeingprocessfrom102submissionswithauthors from 30 countries. In addition, there were four invited talks delivered by Otfried Cheong of KAIST, Korea,...