This project seeks to determine the personal and organizational conditions that are most conducive to the widespread adoption by community-based organizations (CBOs) of effective programs for reducing the spread of HIV and other sexually transmitted infections (STIs). Taking a brief, single-session counseling program (called "Mujer Segura") that has been proven effective in reducing HIV and STIs in female sex workers who work in Mexican cities along the U.S. border, this project will study the implementation of the program in CBOs in 12 additional cities throughout Mexico to determine how best to ensure that the program remains true to the original model and retains its effectiveness. Mexico has been chosen because HIV is a global problem that respects no international borders, and because HIV prevention programs that can be implemented in settings with limited resources are urgently needed in many parts of the world.