Density functional theory (DFT) is increasingly used in biological systems, offering accurate predictions of properties. This review discusses DFT's applications in bioinorganic chemistry, particularly in modeling photosynthesis-related structures and processes. DFT can calculate geometries, energies, reaction mechanisms, and spectroscopic properties. It provides access to a wide range of spectroscopic parameters, including infrared, optical, X-ray absorption, Mössbauer, and magnetic properties. Recent studies highlight DFT's capabilities in these areas, though limitations exist, such as poor performance for certain systems and challenges in accurately predicting electronic states. DFT replaces the many-body wavefunction with the electron density, based on Hohenberg-Kohn theorems. The Kohn-Sham approach is commonly used, involving a non-interacting system with the same density as the original. Approximations like LDA, GGA, and hybrid functionals (e.g., B3LYP) are used, with hybrid functionals often providing better accuracy for transition metal systems. Recent developments include meta-GGA and double-hybrid functionals, which improve energy and spectroscopic predictions. DFT is effective for geometries, with results often matching experimental data. However, weak interactions and certain electronic states are challenging. Hybrid functionals like B3LYP are preferred for accurate predictions, though computational costs can be high. For reaction mechanisms, DFT can locate transition states and predict energy barriers, though accuracy depends on the functional used. Vibrational frequencies calculated with DFT agree well with experimental data, aiding in spectroscopic interpretation. TD-DFT is used for optical spectra, though challenges remain in accurately predicting excited states. X-ray absorption and Mössbauer spectroscopy benefit from DFT, providing insights into electronic and geometric structures. Exchange couplings in magnetic systems are studied using DFT, with hybrid functionals often more accurate. EPR spectroscopy benefits from DFT, though challenges exist in accurately predicting hyperfine coupling. DFT is generally reliable for geometries, vibrational frequencies, and energies, but limitations persist in predicting certain properties. The use of hybrid functionals and careful validation with experimental data is crucial. Future developments aim to improve accuracy in predicting electronic states, magnetic effects, and large systems. DFT remains a powerful tool for bioinorganic studies, though its application requires careful consideration of functional choices and validation against experimental data.Density functional theory (DFT) is increasingly used in biological systems, offering accurate predictions of properties. This review discusses DFT's applications in bioinorganic chemistry, particularly in modeling photosynthesis-related structures and processes. DFT can calculate geometries, energies, reaction mechanisms, and spectroscopic properties. It provides access to a wide range of spectroscopic parameters, including infrared, optical, X-ray absorption, Mössbauer, and magnetic properties. Recent studies highlight DFT's capabilities in these areas, though limitations exist, such as poor performance for certain systems and challenges in accurately predicting electronic states. DFT replaces the many-body wavefunction with the electron density, based on Hohenberg-Kohn theorems. The Kohn-Sham approach is commonly used, involving a non-interacting system with the same density as the original. Approximations like LDA, GGA, and hybrid functionals (e.g., B3LYP) are used, with hybrid functionals often providing better accuracy for transition metal systems. Recent developments include meta-GGA and double-hybrid functionals, which improve energy and spectroscopic predictions. DFT is effective for geometries, with results often matching experimental data. However, weak interactions and certain electronic states are challenging. Hybrid functionals like B3LYP are preferred for accurate predictions, though computational costs can be high. For reaction mechanisms, DFT can locate transition states and predict energy barriers, though accuracy depends on the functional used. Vibrational frequencies calculated with DFT agree well with experimental data, aiding in spectroscopic interpretation. TD-DFT is used for optical spectra, though challenges remain in accurately predicting excited states. X-ray absorption and Mössbauer spectroscopy benefit from DFT, providing insights into electronic and geometric structures. Exchange couplings in magnetic systems are studied using DFT, with hybrid functionals often more accurate. EPR spectroscopy benefits from DFT, though challenges exist in accurately predicting hyperfine coupling. DFT is generally reliable for geometries, vibrational frequencies, and energies, but limitations persist in predicting certain properties. The use of hybrid functionals and careful validation with experimental data is crucial. Future developments aim to improve accuracy in predicting electronic states, magnetic effects, and large systems. DFT remains a powerful tool for bioinorganic studies, though its application requires careful consideration of functional choices and validation against experimental data.