This study was written in March, 2020. It employed a retrospective, cross-sectional observational design to estimate the empirical and unit costs of service provision across the RRTTPR cascade. The analysis utilised gross costing methods applying a top-down approach. The research team obtained cost data from each site for the period October 1, 2016 through September 30, 2017 (referred to as fiscal year 2017 or FY17). This analysis focus on services provided to men who have sex with men (MSM), sex workers (SW), transgender workers (TGW), and people who inject drugs (PWID) based on priorities outlined in the “Collaboration on the Costing of Key Population Interventions to Fast Track the End of HIV in Thailand”. Data were collected from 13 sites and the study conducted in a convenience sample of service delivery sites providing services to MSM, SW, TGW and PWID populations. Three cost components were assessed in this study: a) labor costs b) material cost and c) capital cost