This review paper discusses the normal and superconducting properties of magnesium diboride (MgB₂), a material discovered to exhibit superconductivity at a high critical temperature (Tc) of 40K. MgB₂ is notable for its simple crystal structure, large coherence lengths, high critical current densities, and fields, as well as the transparency of grain boundaries to current flow. The material has been fabricated in various forms, including bulk, single crystals, thin films, tapes, and wires, with the highest critical current densities exceeding 10 MA/cm² and critical fields reaching 40T in thin films. The anisotropy ratio of the upper critical field (γ) is still under debate, ranging from 1.2 to 9, and there is no consensus on the existence of a single or double energy gap. The discovery of superconductivity in MgB₂ has sparked interest in non-oxides and led to searches for superconductivity in related materials, such as TaB₂, BeB₂, and C-S composites. MgB₂'s high Tc makes it a promising material for both large-scale applications and electronic devices, despite its lower Tc compared to high-temperature superconductors (HTSCs). The review also covers topics such as preparation methods, Hall effect, pressure-dependent properties, thermal expansion, effect of substitutions, total isotope effect, Testardi correlation, critical fields, coherence lengths, lower critical fields, irreversibility fields, and critical current density versus applied magnetic field.This review paper discusses the normal and superconducting properties of magnesium diboride (MgB₂), a material discovered to exhibit superconductivity at a high critical temperature (Tc) of 40K. MgB₂ is notable for its simple crystal structure, large coherence lengths, high critical current densities, and fields, as well as the transparency of grain boundaries to current flow. The material has been fabricated in various forms, including bulk, single crystals, thin films, tapes, and wires, with the highest critical current densities exceeding 10 MA/cm² and critical fields reaching 40T in thin films. The anisotropy ratio of the upper critical field (γ) is still under debate, ranging from 1.2 to 9, and there is no consensus on the existence of a single or double energy gap. The discovery of superconductivity in MgB₂ has sparked interest in non-oxides and led to searches for superconductivity in related materials, such as TaB₂, BeB₂, and C-S composites. MgB₂'s high Tc makes it a promising material for both large-scale applications and electronic devices, despite its lower Tc compared to high-temperature superconductors (HTSCs). The review also covers topics such as preparation methods, Hall effect, pressure-dependent properties, thermal expansion, effect of substitutions, total isotope effect, Testardi correlation, critical fields, coherence lengths, lower critical fields, irreversibility fields, and critical current density versus applied magnetic field.