This book constitutes the proceedings of the Third International Workshop on Traffic Monitoring and Analysis, TMA 2011, held in Vienna, Austria, on April 27, 2011 - co-located with EW 2011, the 17th European Wireless Conference. The workshop is an initiative from the COST Action IC0703 "Data Traffic Monitoring and Analysis: Theory, Techniques, Tools and Applications for the Future Networks". The 10 revised full papers and 6 poster papers presented together with 4 short papers were carefully reviewed and selected from 29 submissions. The papers are organized in topical sections on traffic analysis, applications and privacy, traffic classification, and a poster session.