Teen Mental Health First Aid (tMHFA) is an evidence-based program developed in Australia that teaches young people in grades 10-12 how to identify and respond to signs of mental health challenges and crises among peers. Recognizing the growing adolescent mental health crisis in the USA, the National Council for Mental Wellbeing, in partnership with a Johns Hopkins University research team, used a multimethod research approach to adapt the program culturally and contextually from Australia to the USA. The goals of the study were to engage adolescents, MHFA instructors, and content area experts (N = 171) in a process to determine: how to retain the elements of the course that were evidence-based and effective while adapting the program for US students, what topics to add so US students have the essential information and skills teens needed to help a friend experiencing a mental health challenge or crisis, what changes to make to curriculum materials to ensure the style and delivery resonate with US students, and what tools to include so the program is implemented safely and with fidelity in diverse US schools. This paper outlines the adaptation process, including engaging participants, identifying key recommendations for modification, and making changes to the tMHFA program. The findings demonstrate the types of adaptations that may be needed to facilitate implementation and maintenance of program effectiveness when introducing tMHFA to new populations of students in the USA. In addition, the process outlined can be replicated toward this purpose as the program continues to expand both in the USA and in other countries.