A multimodal search engine is designed to imitate the flexibility and agility of how the human mind works to create, process and refuse irrelevant ideas. So, the more elements you have in the input of the search engine to compare, the more accurate the results can be. Multimodal search engines use different inputs of different nature and methods of search at the same time with the possibility of combining the results by merging all of the input elements of the search. There are also engines that can use a feedback of the results with the evaluation of the user to perform a more appropriate and relevant search.

In the present book, ten typical literatures about multimodal information retrieval published on international authoritative journals were selected to introduce the worldwide newest progress, which contains reviews or original researches on multimodal information retrieval. We hope this book can demonstrate advances in multimodal information retrieval as well as give references to the researchers, students and other related people.