The book presents the proceedings of the 30th Biennial Symposium on Communications 2021 (BSC21), a prestigious international research conference in communications, information theory, and signal processing. Started in 1962 by Queen's University, Canada, the Symposium is now presented by the Canadian Society of Information Theory. Its 30th edition was hosted virtually by The University of Saskatchewan and held in Saskatoon from June 28 to 30, 2021. Topics include Communication and Information Theory, Coding and Signal Processing for Communications, and Multiple Antenna Systems and Cooperative Communications.