ESSAI & ACAI-2023 follow on the footsteps of ACAI (Advanced Course on AI) and the TAILOR Summer School on AI. ACAI is organized since 1985 under the auspices of EurAI, The European Association for Artificial Intelligence, and ACAI-2023 will be its 20th edition. The TAILOR Summer School on AI is associated with the EU Project TAILOR (Foundations of Trustworthy AI – Integrating Reasoning, Learning and Optimization). Its first edition in 2021 was standalone and virtual, in 2022 it was organized in Barcelona together with ACAI, and this third edition is special as it grows into ESSAI-2023, The First European Summer School on AI. ESSAI & ACAI-2023 will take place at the Faculty of Computer and Information Science, University of Ljubljana. They will comprise 30 courses/ tutorials, presented in six parallel tracks. ACAI-2023 will offer 10 invited tutorials (of 2x90min each) on the topic of AI & Science, while ESSAI-2023 will offer 20 courses (of 5x90min each) on all topics of AI, solicited through an open call for course proposals and selected by an international program committee.