Ant-colony optimization (ACO) is an algorithm of metaheuristics inspired by the foraging behaviour of ants. ACO is being widely used for solving various problems of optimisation, which includes combinatorial problems of optimisation, linear programming problems, network problems of optimisation. Recently, ACO has been successfully combined with other optimization algorithms to improve their performance. This paper tends to provide a detailed review of the usage of ACO with other optimization algorithms, such as branch and bound (B&B), cutting-plane algorithm, transportation model, network model. The paper also discusses the advantages of using ACO with other optimization algorithms, such as the ability to diversify the search, improvement of convergence speed and finding good quality solution. The paper concludes by presenting some open challenges and future research directions in the area of ACO and other optimization algorithms.