On behalf of the Thai Physics Society and the Organizing Committee, it is my great pleasure to welcome all participants to the 21^st Siam Physics Congress 2026 (SPC2026). This annual conference continues to serve as Thailand’s flagship event for physicists, researchers, and professionals from across disciplines to share knowledge, exchange ideas, and foster collaborations that drive scientific and technological progress.

On behalf of the Organizing Committee, it is both an honor and a privilege to welcome you to the 21^st Siam Physics Congress (SPC2026), which will take place from 20^th to 22^nd May 2026, at the Dusit Thani Hua Hin, Phetchaburi, Thailand. As Chairman of SPC2026 and SPC2026 committees, we are very excited to bring together physicists, researchers, educators, and students from around the world for this premier gathering a platform where collaboration, innovation, and groundbreaking research in physics take center stage.