Global optimization has a wide range of applications, including chemistry, engineering, biology, economics, and physics. It includes a broad range of optimization problems, where both continuous and discrete variables are involved. Unlike many optimization methods that find locally optimal solutions, global optimization methods guarantee a globally optimal solution that is intrinsically difficult to find as there might exists multiple local optima. In this survey article, we make an appraisal of the existing state of affairs in global optimization. We discuss the theoretical and algorithmic advances made in the past decades in the area of global optimization.