The Emergency Service Mobile Communications Programme (ESMCP) has the challenge ahead of it to define the performance, operational, and security requirements that will assure the successful deployment of the next generation of communications for the emergency services within the UK. This session will focus on the process undertaken by the U.S. Emergency Services in defining the requirements for their nationwide network called FirstNet. The session will discuss important requirements identified by the requirements process, lead by the U.S. National Institute of Standards (NIST), with a focus on the critical network services identified as a result of the activity. These critical functions were deemed by the user base to be necessary for providing agencies confidence in any future systems ability to meet their operational needs.