Siyan is a community and global health epidemiologist by training and a pioneer in population health research in Southeast Asia. He is an Assistant Professor and the UHS-SSHSPH Integrated Research Program Lead (USIRP) at Saw Swee Hock School of Public Health, National University of Singapore. He serves as the founding Director of the KHANA Center for Population Health in Cambodia and Adjunct Professor at the Center for Global Health Research, Touro University California. He received his Medical Doctor (MD) degree from the University of Health Sciences in Cambodia and a PhD degree in International Health from the University of Tokyo. He established the KHANA Center for Population Health Research in 2015 after spending several years at Japan’s National Center for Global Health and Medicine, University of South Australia, and Stanford University. His research explores effective community-based interventions to improve access to health care services among vulnerable and marginalized populations. His ongoing projects include the BMGF-funded i-MoMCARE project and five large-scale community-based randomized controlled trials on HIV, tuberculosis, and gender-based violence. He sits in several national and international technical working groups, has published more than 100 research articles, and is the winner of six international research awards.