This book constitutes the refereed proceedings of the 21st International Conference on Advances in Mobile Computing and Multimedia Intelligence, MoMM2023, organized in conjunction with the 25th International Conference on Information Integration and Web Intelligence, iiWAS 2023, held in Denpasar, Bali, Indonesia, during December 4-6, 2023. The 10 full papers and 5 short papers presented in this book were carefully reviewed and selected from 37 submissions. The papers are divided into the following topical sections: security in mobile environments; mobile computing and wireless sensors; and image and video processing.