The concept of "Mission Critical Push To Talk" (MCPTT) has been specified in 3GPP Release 13. Interoperability and MCPTT service harmonization are critical challenges to be taken into account for the successful deployment and operation of Mission Critical Communication. The event was held at the ETSI headquarters in Sophia Antipolis, France on 23 June 2017 with 140 participants from 19 vendors. Push-to-Talk (PTT) is a standard feature of narrowband Professional Mobile Radio (PMR) technologies developed specifically for mission-critical communications. PTT enables near instantaneous group communications – a critical requirement in an emergency situation. To ensure that such capability is built in to LTE services, 3GPP has been catalyzed by the work of the TCCA to ensure that LTE supports mission-critical communications, with MCPTT now specified in 3GPP Release 13. More than 1000 tests were conducted, with a success rate of 85%. The tests are based on 3GPP, ETSI and IETF standards. For this first session, a test specification has been developed for the 3GPP Release 13 MCPTT, comprising 47 test cases. Although the PMR market shows no signs of slowing, mission-critical broadband LTE will offer complementary capabilities, and its market is expected to grow at a compound annual growth rate of 20 per cent, from $1.1 billion in 2015 to $2.6 billion in 2020. Planned nationwide rollouts in the United States, South Korea, the UK, the Middle East and Asian countries are expected to trigger significant large-scale investments in mission-critical LTE.