Book excerpt: This book constitutes the refereed conference proceedings of the 13th International Conference on Bio-inspired Information and Communications Technologies, held in September 2021. Due to the safety concerns and travel restrictions caused by COVID-19, BICT 2021 took place online in a live stream. BICT 2021 aims to provide a world-leading and multidisciplinary venue for researchers and practitioners in diverse disciplines that seek the understanding of key principles, processes and mechanisms in biological systems and leverage those understandings to develop novel information and communications technologies (ICT). The 20 full and 2 short papers were carefully reviewed and selected from 47 submissions. The papers are organized thematically in tracks as follows: Bio-inspired network systems and applications; Bio-inspired information and communication; mathematical modelling and simulations of biological systems.