Axions are a class of particles that play a significant role in cosmology and high-energy physics. They are motivated by theories addressing the strong-CP problem, supersymmetry, and extra dimensions, including string theory. This review explores axion cosmology, focusing on their role in dark matter, dark radiation, the cosmological constant problem, and their interactions with astrophysical phenomena. Axions are considered as ultralight particles with masses in the range $10^{-33}$ eV to $10^{-18}$ eV, which makes them viable dark matter candidates. The review discusses the production of axions during inflation, their cosmological evolution, and their interactions with the standard model. It also covers the constraints on axion mass and relic density from cosmological observations, including the cosmic microwave background and large-scale structure. The review highlights the potential of axions to explain structure formation and reionization, and their role in the cosmological constant problem. Axions are also discussed in the context of black hole superradiance, astrophysical magnetic fields, and their interactions with pulsars. The review emphasizes the importance of precision cosmology in constraining axion properties and the potential for future experiments to detect axions. The review also addresses the challenges in detecting axions, including their weak coupling to standard model particles and the need for high-precision measurements. Overall, axions offer a unique window into fundamental physics and cosmology, with implications for dark matter, dark energy, and the early universe.Axions are a class of particles that play a significant role in cosmology and high-energy physics. They are motivated by theories addressing the strong-CP problem, supersymmetry, and extra dimensions, including string theory. This review explores axion cosmology, focusing on their role in dark matter, dark radiation, the cosmological constant problem, and their interactions with astrophysical phenomena. Axions are considered as ultralight particles with masses in the range $10^{-33}$ eV to $10^{-18}$ eV, which makes them viable dark matter candidates. The review discusses the production of axions during inflation, their cosmological evolution, and their interactions with the standard model. It also covers the constraints on axion mass and relic density from cosmological observations, including the cosmic microwave background and large-scale structure. The review highlights the potential of axions to explain structure formation and reionization, and their role in the cosmological constant problem. Axions are also discussed in the context of black hole superradiance, astrophysical magnetic fields, and their interactions with pulsars. The review emphasizes the importance of precision cosmology in constraining axion properties and the potential for future experiments to detect axions. The review also addresses the challenges in detecting axions, including their weak coupling to standard model particles and the need for high-precision measurements. Overall, axions offer a unique window into fundamental physics and cosmology, with implications for dark matter, dark energy, and the early universe.