This chapter introduces the concept of “search space” which determines the set of admissible solutions to a given optimization problem. The search space, together with the specification of the function that needs to be maximized or minimized, defines uniquely an optimization problem. This chapter presents the important definitions related to the optimization goal, explaining what metaheuristics are and how they work to address such problems. Several examples of search spaces associated with classical optimization problems are given, as well as basic metaheuristics.