Multi-agent systems have unique failure modes. The MAST taxonomy categorizes them: Misrouting (wrong agent for task), Amplification (errors compound through the system), Stagnation (agents loop without progress), and Termination (premature stopping or infinite loops). Error amplification is particularly dangerous—each agent may add to a previous agent's error, making small mistakes catastrophic. Cascade failures occur when one agent's failure causes downstream agents to fail. Circuit breakers stop cascades. Graceful degradation provides partial value when full orchestration fails.