This hallmark text presents both theoretical and practical foundations of Ant Colony Optimization (ACO) along with its applications. The research orientation in the book provides possible modifications and enhancements of conventional ACO and the superiority of Hybrid approaches. An efficient Hybrid Technique "Nested Hybrid ACO" deals with a complex and popular combinatorial optimization problem, Travelling Salesman Problem(TSP). The comparison with state-of-the-art algorithms for solving TSP proves the superiority of the hybrid approaches, which is very much useful to the research community. The strength of this book is easy explanation, exhaustive literature survey, supported simulation results with analysis, rich comparative study and future research direction.