This book constitutes the refereed proceedings of the Third International Meeting on Innovation for Systems Information and Decision, INSID 2021, which was held during December 1-3, 2021. The conference was initially planned to take place in Recife, Brazil, but changed to a virtual meeting due to the COVID-19 pandemic.

The 9 full papers presented in this volume were carefully reviewed and selected from a total of 76 submissions. They reflect methodological improvements and advances in multi-criteria decision-making/multi-criteria decision-aid (MCDM/MCDA) oriented toward real-world applications, which contribute to the understanding of relevant developments of current research on and future trends of innovation for systems information and decision.