The OECD's Survey on Social and Emotional Skills (SSES) 2023 represents the largest global initiative to gather comparable data on the development of social and emotional skills among 10- and 15-year-old students. In the 2023 cycle of SSES, 16 sites implemented an assessment of students' social and emotional skills and collected contextual information from students, teachers, school principals, and, optionally, parents using standardised, uniform procedures that ensure the results are comparable and meaningful. This Technical Report has been prepared by those who implemented SSES during its 2023 cycle to provide transparency on the procedures and statistical methods that underpin the comparability and validity of the SSES 2023 results.