This lecture covers the Ant Colony Optimization (ACO) metaheuristic, focusing on the Ant Colony System (ACS) algorithm and its extensions. Topics include constructive heuristics, local search algorithms, pheromone trail mechanisms, candidate lists, and comparisons with other optimization algorithms. The lecture also delves into the application of ACO in communication networks, routing algorithms, and real-world scenarios. Theoretical results, real-world applications, and literature references are discussed, highlighting the effectiveness of ACO in solving complex combinatorial optimization problems.