The achievement in twenty years is not a minor one. A huge leap of achievement has been enhanced, from zero to 4.0 early warning and mitigation system. With nonexistence of a warning system and lack of people’s awareness and preparedness for tsunami caused over 230 thousand people killed in the region during the 2004 devastated Indian Ocean tsunami. To respond to this event, a warning system was established in 2005 under the mandate of the Resolution of UNESCO IOC-XXIII-12, named Indian Ocean Tsunami Warning and Mitigation System. The principles of people centre and end-to-end approaches were used in the development of the early warning system, showing the responsibility sharing among regional, national and local stakeholders for each warning function. Currently, the 4.0 hazard detection and forecast are led by Australia, India and Indonesia as tsunami service provider for the 24 member countries in Indian Ocean, as well as using 4.0 technology for threat evaluation and alert formulation to warn their people at risk. However, biggest challenges remain at the downstream component to respond to the global commitment that by 2030 all the people living at tsunami prone area should be prepared and be resilient and all the tsunami prone area should be protected by early warning system.