The 4th International Conference of the Asian Society for Precision Engineering and Nanotechnology (ASPEN) was organised by the Partner State Key Laboratory of Ultra Precision Machining Technology of The Hong Kong Polytechnic University from 16th to 18th November 2011. The event was officiated by Professor Timothy W. Tong, President of The Hong Kong Polytechnic University, Professor Hu Xiaotang, Vice-President of Tianjin University, Professor Jin Guofan, Academician of Chinese Academy of Engineering, TsinghuaUniversity, and Professor W.B. Lee, Conference General Chair and President of ASPEN. The conference successfully attracted over 300 participants from more than 50 institutions and organizations around the world. A total of 192 papers were presented. For more details and photographs of the conference, visit: http://www.aspen2011.com/snaps.php.