This talk will cover the nuts and bolts of tsunami science and how tsunami warning systems work. This includes how tsunamis are generated, how they propagate across ocean basins and why they are destructive. Most destructive tsunamis are generated by great earthquakes. Therefore tsunami warning centers have developed methods to rapidly analyze earthquakes and assess their potential to generate destructive tsunamis. Tsunami warning centers act as the trip wire i.e., they rapidly pass on the results of their analysis to National or State Disaster Organizations (like FEMA or State Civil Defense agencies) whose task it is to make sure the public at risk receives the warnings (sound sirens for example) and facilitate evacuations.