Abstract: We address the problem of unsupervised video activity classification and detection. Different from previously existing methods proposed for this task, we present a space-time link- analysis approach which consistently matches or exceeds the performance of traditional unsupervised activity classification methods in various datasets. Our method is inspired by the recent success of link-analysis techniques in the image domain. By applying these techniques in the space-time domain, we are able to naturally take into account the spatial-temporal relationships among the video features, while leveraging the power of graph matching for activity classification. We present a set of experiments demonstrating that our approach is capable of handling cluttered backgrounds, activities with subtle movements, and video data from moving cameras using standard datasets. We also demonstrate our method in a surveillance application with the goal of avoiding fraud in retail stores. Ming-Ting Sun received the B.S. degree from National Taiwan University in 1976, the M.S. degree from University of Texas at Arlington in 1981, and the Ph.D. degree from University of California, Los Angeles in 1985, all in electrical engineering. He joined the University of Washington in August 1996 where he is a Professor. Previously, he was the Director of the Video Signal Processing Research Group at Bellcore. He was a chaired professor at TsingHwa University (Beijing) and a visiting professor at Tokyo University. He holds 11 patents and has published over 200 technical papers, including 16 book chapters in the area of video and multimedia technologies. He co-edited a book “Compressed Video over Networks”. He was the Editor- in-Chief of the IEEE Transactions on Multimedia (TMM) and a Distinguished Lecturer of the Circuits and Systems Society from 2000 to 2001. He received an IEEE CASS Golden Jubilee Medal in 2000, and was the general co-chair of the Visual Communications and Image Processing 2000 Conference. He was the Editor-in- Chief of the IEEE Transactions on Circuits and Systems for Video Technology (TCSVT) from 1995 to 1997. He received the TCSVT Best Paper Award in 1993. From 1988 to 1991, he was the chairman of the IEEE CAS Standards Committee and established the IEEE Inverse Discrete Cosine Transform Standard. He received an Award of Excellence from Bellcore for his work on the digital subscriber line in 1987. He is a Fellow of IEEE.