This document summarizes a lecture on multi-robot systems. It discusses why multi-robot systems are used, including for robustness, scalability, performance, and specialization. It covers reactive coordination algorithms inspired by ant colonies, which use indirect communication via pheromone trails. It also discusses deliberative coordination through the example of yacht racing crews. Key lessons are that multi-robot systems distribute sensing, computation and communication, and coordination algorithms are probabilistic approaches based on available capabilities.