We identified 50 of the largest multi-party cyber incidents over the past several years in an effort to understand their causes and consequences from beginning to end. Tsunami draws from the same rigorous methodology in the rest of the IRIS series. We started with a huge dataset of cyber loss events, identified those that involved multiple organizations, and then researched each event to understand who was behind it, what happened, how the after effects propagated through the supply chain, and the financial losses for all parties involved.