This review discusses recent significant research developments on the layered perovskite Sr₂RuO₄, focusing on both experimental and theoretical perspectives. Since its discovery of superconductivity in 1994, Sr₂RuO₄ has been recognized as an archetypal unconventional superconductor among strongly correlated electron systems. Initially, it was thought to exhibit a spin-triplet chiral p-wave superconducting state, which breaks time-reversal symmetry. However, in 2019, new experimental results overturned this belief, suggesting a spin-singlet-like behavior. Innovations in uniaxial strain devices have allowed researchers to explore changes in the superconducting state by controlling the symmetry and dimensionality of the Fermi surfaces, enhancing the superconducting transition temperature (Tc) from 1.5 K to 3.5 K. A spin-singlet chiral d-wave superconducting state is consistent with most recent experimental findings. However, there are still unresolved aspects that need explanation. The review highlights the need to go beyond traditional frameworks and consider the multi-orbital aspects of the electronic states to fully understand the superconducting state of Sr₂RuO₄. It covers the normal state properties, spin susceptibility, superconducting gap structure, phase-sensitive experiments, and theoretical models, aiming to resolve the remaining mysteries and provide a comprehensive overview of the current status and open questions in the field.This review discusses recent significant research developments on the layered perovskite Sr₂RuO₄, focusing on both experimental and theoretical perspectives. Since its discovery of superconductivity in 1994, Sr₂RuO₄ has been recognized as an archetypal unconventional superconductor among strongly correlated electron systems. Initially, it was thought to exhibit a spin-triplet chiral p-wave superconducting state, which breaks time-reversal symmetry. However, in 2019, new experimental results overturned this belief, suggesting a spin-singlet-like behavior. Innovations in uniaxial strain devices have allowed researchers to explore changes in the superconducting state by controlling the symmetry and dimensionality of the Fermi surfaces, enhancing the superconducting transition temperature (Tc) from 1.5 K to 3.5 K. A spin-singlet chiral d-wave superconducting state is consistent with most recent experimental findings. However, there are still unresolved aspects that need explanation. The review highlights the need to go beyond traditional frameworks and consider the multi-orbital aspects of the electronic states to fully understand the superconducting state of Sr₂RuO₄. It covers the normal state properties, spin susceptibility, superconducting gap structure, phase-sensitive experiments, and theoretical models, aiming to resolve the remaining mysteries and provide a comprehensive overview of the current status and open questions in the field.