Guatemala is a major transit point for drugs bound for the United States and the recipient of U.S. counternarcotics aid and technical assistance, much of which is provided through U.S. Southern Command (USSOUTHCOM) and U.S. Army South. As a first step by Guatemala in putting this aid to work toward developing its own counternarcotics capacity, the president of Guatemala established the Interagency Task Force (IATF) Tecún Umán. USSOUTHCOM has expressed the intent to apply the IATF as a model to other similarly porous border regions in the area. Thus, documenting and using lessons from the IATF Tecún Umán will help in the development of new and similar units. This report is intended to support that lessons-learned function, demonstrate how these preliminary lessons are being applied to future IATF development, and provide recommendations on how to resolve remaining IATF challenges.