Interoperability between US border towns and their Mexican sister-cities remains a challenge for both US and Mexican government agencies. In addition to differences in government structure, there are political, security, and historical concerns that may prevent county-level emergency managers from collaborating with counterparts from either the Mexican municipalities or the state. There are opportunities to overcome these challenges, but these challenges are ongoing and require significant effort from agencies on both sides of the border to keep collaboration and communication pathways current and effective. This document provides suggested best practices derived from a case study where the County of San Diego’s Office of Emergency Services established a positive working relationship with their counterparts in the Tijuana’s Departmento Proteccion Civil Municipal, the State of Baja California Proteccion Civil, and the overall Centro de Control, Comando, Comunicación y Cómputo (C4). This document details how this case study provided the means by which these relationships were built during the planning and creation of an Emergency Cross-Border Communication Concept of Operations (ECBC CONOPS) document. Despite the ECBC CONOPS development in the midst of the one the busiest land Ports-of-Entry in the world where multiple federal, state, and local working agreements already exist, local government interoperability gaps still exist at the operational level. The intent of the ECBC CONOPS project was to bridge the gaps in emergency operational communication and coordination at the County of San Diego and Municipality of Tijuana level and the State of Baja California levels. Gaps that would need to be overcome would likely appear during regional cross-border emergencies impacting communication systems such as cross-border fires, earthquakes, power-outages, and severe weather events. The communication protocols established during this endeavor facilitate on-going efforts for additional cross-border training and coordination. Ultimately, it is the hope of the author that the suggested best practices described in this document will provide an avenue towards broader interoperability and collaboration for other sister cities and agencies along the US-Mexico international border.