The 18th Siam Physics Congress (SPC2023) was successfully held during 14–16 June 2023, co-hosted by the Thai Physics Society and the Chiang Mai University. To motivate collaborative academic environment, the congress was organized to be a 100% on-site meeting at the Empress Convention Center in Chiang Mai (Thailand).This year, we had 329 research abstracts submitted for both oral and poster presentations. There were 3 plenary speakers, 17 invited speakers, 110 accepted oral presentations, 187 accepted poster presentations, and 116 full papers submitted for possible publication in all 10 tracks(topics). The scientific program was announced on the SPC2023 website (https://spc2023.science.cmu.ac.th) and also distributed via email to all participants.The opening ceremony was given by the President of Thai Physics Society and the President of Association of Asia Pacific Physical Societies (AAPPS). After opening ceremony, Prof. Dr. Junichi Yokoyama (The University of Tokyo, Japan) gave the 1st plenary talk (onsite), Prof. Dr. Jian-Wei Pan (University of Science and Technology of China) gave this 2nd plenary talk (zoom), Assoc. Prof. Dr. Tawatchai Onjun (Thailand Institute of Nuclear Technology) gave the 3rd plenary talk (onsite), where the size of the audience attending the plenary talks is approximately 500 participants. The oral presentations were arranged into 5 parallel rooms in total of 10 sessions. Each invited speaker was allowed 30-minutes presentation while regular presenter had 15 minutes including questions and answers. The audience-size of each room varied between 30 and 50 people. The poster presentations were held in the poster hall and lasted for 2 hours, which offered extended opportunity to gain insights into the latest research. For full papers, authors of accepted abstracts were invited to submit their full-scale works through the Morressier website for a possible publication in the Journal of Physics : Conference Series.List of Topic, Plenary Speaker, Organizing Institutions, Advisory Committee, Organizing Committee, Scientific Committee, Ceremony Committee, Finance Committee, Registration Committee, Venue and Transportation Committee, Sponsorship and Fundraising Committee, Public Relations Committee, Audio Visual Aid Committee, Sponsors are available in this Pdf.