Sustainable energy planning is essential for enhancing security, addressing climate change, and promoting economic growth. The penetration of renewable energy resources into power systems is crucial for moving toward an eco-friendly grid. In this context, sustainable energy planning stands as a pivotal point. This chapter investigates the optimization techniques in sustainable energy planning, describing the challenges and opportunities that renewable energy resources offer to power systems. In the following chapter, various methods such as linear and nonlinear programming, multi-objective optimization, stochastic techniques, and metaheuristic approaches are reviewed. The chapter also explores the emerging paradigms of novel data-driven and AI-powered algorithms into renewable energy planning purposes. Optimization methods are compared across various facets, and conclusions are drawn. Furthermore, the chapter discusses famous sustainable planning objectives, including environmental, technical, economic, and societal assessments which are essential for the development of a sustainable power system. By presenting the advantages and limitations of different optimization techniques, this chapter equips system planners, decision-makers, and researchers with the knowledge to address the complexities of shifting toward sustainable and renewable energy networks in future power grids.