This book contains a selection of revised papers from the 4th Workshop on Machine Learning for Multimodal Interaction (MLMI 2007), which took place in Brno, Czech Republic, during June 28-30, 2007. As in the previous editions of the MLMI series, the 26 chapters of this book cover a large area of topics, from multimodal processing and human-computer interaction to video, audio, speech and language processing. The application of machine learning techniques to problems arising in these ?elds and the design and analysis of software s- portingmultimodalhuman-humanandhuman-computerinteractionarethetwo overarching themes of this post-workshop book. The MLMI 2007 workshop featured 18 oral presentations-two invited talks, 14 regular talks and two special session talks-and 42 poster presentations. The participants were not only related to the sponsoring projects, AMI/AMIDA (http://www.amiproject.org) and IM2 (http://www.im2.ch), but also to other largeresearchprojects onmultimodalprocessingand multimedia browsing,such as CALO and CHIL. Local universities were well represented, as well as other European, US and Japanese universities, research institutions and private c- panies, from a dozen countries overall.