The fourth rung of Jacob's Ladder introduces hybrid functionals, which blend a portion of the exact exchange energy from Hartree-Fock theory with DFT calculations. Hybrid functionals, such as B3LYP (Becke, threeparameter, Lee-Yang-Parr), are widely regarded for their accuracy in predicting molecular geometries, bond energies, and vibrational frequencies . By incorporating a fraction of exact exchange, hybrid functionals correct for some of the deficiencies of pure DFT functionals, such as delocalization errors and underestimation of excitation energies. Hybrid methods are extensively used in quantum chemistry for both organic and inorganic systems, although their computational cost is higher than GGA and Meta-GGA functionals. At the top of the ladder lies the fifth rung: Double-Hybrid Functionals. These functionals incorporate not only Hartree-Fock exchange but also perturbative correlation energy from methods like second-order Møller-Plesset perturbation theory (MP2) . Double-hybrid functionals, such as B2PLYP, offer the highest level of accuracy among commonly used DFT methods, particularly for thermochemistry and reaction energetics. However, their increased computational cost limits their application to smaller systems. Despite this, double-hybrids represent the pinnacle of Jacob's Ladder, providing unprecedented accuracy for complex systems, especially those with significant electron correlation effects, such as excited states or transition metals. This hierarchical framework of Jacob's Ladder is invaluable for researchers as it provides a clear guide for selecting the appropriate functional based on the trade-off between computational cost and accuracy. For systems where computational resources are limited or where approximate results are sufficient, functionals from the lower rungs, such as GGA or Meta-GGA, are suitable. However, when high accuracy is paramount, as in reaction energy calculations or electronic structure predictions for complex systems, higher-rung functionals like hybrids or double-hybrids are preferred. In recent years, there has been significant progress in refining functionals at each rung of the ladder. Newer hybrid and meta-GGA functionals, such as SCAN (Strongly Constrained and Appropriately Normed), have shown promise in improving the accuracy of DFT calculations for a wide range of systems, from small organic molecules to complex materials . These advancements are pushing the boundaries of what DFT can achieve, narrowing the gap between computational and experimental results, and further solidifying the importance of Jacob's Ladder as a guiding principle in the evolution of DFT.