<p>The economic dispatch (ED) problem is one of the core optimization problems designed for the optimal operation of the power system. This problem aims to determine the optimal scheduling of the generating units such that the operating cost of power generation is minimum while all operational constraints are satisfied. With the increasing electricity demand, growing integration of renewable energy sources, and environmental concerns, the traditional ED problem has evolved into a complex, nonlinear, non-convex, and multi-objective optimization problem. To solve this complex problem, numerous conventional and meta-heuristic optimization techniques have been developed. To understand the recent trend and ongoing research challenges in this field, this article presents a comprehensive review of the ED problem. This article reviews the evolution of ED problem formulations, operational constraints associated with them, and recent methodologies developed to address this challenging problem. Finally, the article identifies existing research gaps, emerging challenges, and future research opportunities. Overall, this article provides researchers with a structured and comprehensive understanding of modern ED problems and solution methodologies by synthesizing findings from more than one hundred studies published over the past few years. Unlike existing reviews that primarily focus on optimization algorithms, this work provides an integrated analysis of ED formulations, their operational constraints, and emerging intelligent energy management strategies. Further, this review also offers a road map for the development of next-generation ED solutions for renewable-rich and intelligent power systems.</p>