This book constitutes the refereed proceedings of the 17th International Conference on Mobile Web and Intelligent Information Systems, MobiWIS 2021, held as a virtual event, in August 2021. The 15 full papers presented in this book were carefully reviewed and selected from 40 submissions. The papers of MobiWIS 2021 deal focus on topics such as security and privacy; web and mobile applications; networking and communication; intelligent information systems; and IoT and ubiquitous computing.