At its 10th Session held in Muscat, Oman in March 2015, the Intergovernmental Coordination Group for the Indian Ocean Tsunami Warning and Mitigation System (ICG/IOTWMS) decided to organise an Indian Ocean Wave Exercise (IOWave16) in 2016 and established a Task Team to plan and conduct the exercise. At its recent intersessional meeting held in Hyderabad, India on 13th November, the Task Team decided to conduct the IOWave16 exercise on 7th and 8th September 2016. This letter provides details of the exercise in which all IOTWMS Member States are encouraged to participate to the extent possible. Exercise IOWave16 will simulate Indian Ocean countries being put in a tsunami warning situation and require the National Tsunami Warning Centre (NTWC) and the National and/or Local Disaster Management Offices (NDMO/LDMO) in each country to implement their Standard Operating Procedures (SOP). A significant observation from Exercise IOWave14, held in September 2014, was that only three countries included any form of community evacuation drill in the exercise. A primary objective of IOWave16 therefore is to encourage more countries to involve coastal communities in the exercise to test the SOPs and communications links at all levels of the warning chain. The exercise will comprise two scenarios on successive days, one in the eastern Indian Ocean and the other in the northwestern Indian Ocean. The first scenario will simulate a magnitude 9.2 earthquake south of Sumatra, Indonesia and the second scenario will simulate a magnitude 9.0 earthquake in the Makran Trench south of Iran and Pakistan. Both scenarios will generate simulated tsunami waves travelling across the Indian Ocean basin. The south of Sumatra scenario will commence at 0300 hours UTC on 7th September and the Makran Trench scenario will commence at 0600 hours UTC on 8th September. Member States are invited to participate in either or both events, which will run in real time. The IOTWMS Tsunami Service Providers (TSP) of Australia, India and Indonesia will provide exercise bulletins and detailed tsunami threat advice on their password-protected websites, and will send Notification Messages to the Tsunami Warning Focal Points (TWFP) as the data is updated during the events. An IOWave16 Exercise Manual will be distributed by the end of March 2016 with further details of the exercise scenarios and the exercise evaluation to be conducted afterwards.