This review discusses the superconducting properties of magnesium diboride (MgB₂), a material known since the 1950s but recently found to be superconducting at a remarkably high critical temperature of 40 K. MgB₂ is notable for its high Tc, simple crystal structure, large coherence lengths, high critical current densities, and transparent grain boundaries, making it a promising material for both large-scale applications and electronic devices. Over the past seven months, MgB₂ has been synthesized in various forms, including bulk, single crystals, thin films, tapes, and wires. Thin films have achieved the highest critical current densities (>10 MA/cm²) and critical fields (40 T). However, the anisotropy ratio of the upper critical field remains unresolved, with values ranging from 1.2 to 9. There is also no consensus on whether MgB₂ has a single or double energy gap. MgB₂ holds the record for the highest Tc among simple binary compounds. The discovery of superconductivity in MgB₂ has reignited interest in non-oxide superconductors and led to the search for superconductivity in related materials, such as TaB₂, BeB₂.₇₅, C-S composites, and elemental boron under pressure. The structure of MgB₂ consists of graphite-type boron layers separated by hexagonal close-packed magnesium layers. The material exhibits strong anisotropy in B-B distances and has a transition temperature nearly twice that of the highest Tc in binary superconductors. The discovery of superconductivity in MgB₂ has sparked significant research into its properties, including its Hall coefficient, pressure dependence, and critical fields. MgB₂ shows a positive Hall coefficient, indicating hole-like charge carriers. The critical temperature of MgB₂ decreases under pressure, with different samples showing varying rates of decrease. The anisotropy of the upper critical field is still unresolved, with values ranging from 1.1 to 9. The material's high critical current densities and fields make it a promising candidate for applications, and its superconducting properties are influenced by its layered structure and the role of metallic boron layers. The review also discusses the effects of substitutions on the critical temperature of MgB₂, the total isotope effect, and the Testardi correlation between Tc and resistivity ratio. MgB₂ exhibits a phonon-mediated superconducting mechanism, with significant contributions from boron vibrations. The critical fields of MgB₂ vary depending on the material's configuration, with films showing the highest upper critical fields. The anisotropy of the upper critical field is still a topic of debate, with some studies suggesting values as high as 6-9. Overall, MgB₂ is a promising material for superconducting applications due to its high Tc, large critical current densities, and unique properties.This review discusses the superconducting properties of magnesium diboride (MgB₂), a material known since the 1950s but recently found to be superconducting at a remarkably high critical temperature of 40 K. MgB₂ is notable for its high Tc, simple crystal structure, large coherence lengths, high critical current densities, and transparent grain boundaries, making it a promising material for both large-scale applications and electronic devices. Over the past seven months, MgB₂ has been synthesized in various forms, including bulk, single crystals, thin films, tapes, and wires. Thin films have achieved the highest critical current densities (>10 MA/cm²) and critical fields (40 T). However, the anisotropy ratio of the upper critical field remains unresolved, with values ranging from 1.2 to 9. There is also no consensus on whether MgB₂ has a single or double energy gap. MgB₂ holds the record for the highest Tc among simple binary compounds. The discovery of superconductivity in MgB₂ has reignited interest in non-oxide superconductors and led to the search for superconductivity in related materials, such as TaB₂, BeB₂.₇₅, C-S composites, and elemental boron under pressure. The structure of MgB₂ consists of graphite-type boron layers separated by hexagonal close-packed magnesium layers. The material exhibits strong anisotropy in B-B distances and has a transition temperature nearly twice that of the highest Tc in binary superconductors. The discovery of superconductivity in MgB₂ has sparked significant research into its properties, including its Hall coefficient, pressure dependence, and critical fields. MgB₂ shows a positive Hall coefficient, indicating hole-like charge carriers. The critical temperature of MgB₂ decreases under pressure, with different samples showing varying rates of decrease. The anisotropy of the upper critical field is still unresolved, with values ranging from 1.1 to 9. The material's high critical current densities and fields make it a promising candidate for applications, and its superconducting properties are influenced by its layered structure and the role of metallic boron layers. The review also discusses the effects of substitutions on the critical temperature of MgB₂, the total isotope effect, and the Testardi correlation between Tc and resistivity ratio. MgB₂ exhibits a phonon-mediated superconducting mechanism, with significant contributions from boron vibrations. The critical fields of MgB₂ vary depending on the material's configuration, with films showing the highest upper critical fields. The anisotropy of the upper critical field is still a topic of debate, with some studies suggesting values as high as 6-9. Overall, MgB₂ is a promising material for superconducting applications due to its high Tc, large critical current densities, and unique properties.