This book contains extended versions of research papers presented at the international sessions at the 35th Annual Conference of the Japanese Society for Artificial Intelligence (JSAI2021), which was held online from June 8-11, 2021. The JSAI annual conferences are considered key events for our organization, and the international sessions held at these conferences play a key role for the society in its efforts to share Japan's research on artificial intelligence with other countries. The topics of the international sessions in JSAI2021 cover five categories: knowledge engineering, machine learning, agents, robots and real worlds, and human interface and education aid. From the papers submitted to those categories, papers of high quality were selected through the strict reviewing procedure. As a result, 19 papers are included in this book. From this book, readers can get an overview of recent Japan's research on artificial intelligence.

This book constitutes the refereed proceedings of the 23rd International Conference on Principles and Practice of Multi-Agent Systems, PRIMA 2020, held in Nagoya, Japan, in November 2020. The 19 full papers presented and 13 short papers were carefully reviewed and selected from 50 submissions.Due to COVID-19, the conference was held online. The conference covers a wide range of ranging from foundations of agent theory and engineering aspects of agent systems, to emerging interdisciplinary areas of agent-based research.