Cosmic strings are topological defects that may have formed during phase transitions in the early universe, analogous to vortex lines in liquid helium or flux tubes in superconductors. They are predicted by some unified theories of particle interactions and could explain large-scale structures in the universe. This review covers the background from particle physics and cosmology, the dynamics and interactions of cosmic strings, their formation and evolution in the early universe, observational implications, and the current status of the theory. Cosmic strings are massive objects with very high energy per unit length, and their gravitational effects can explain the observed fluctuations in the cosmic microwave background and matter distribution. The review also discusses the different types of cosmic strings that can form in various field theories, including global and local (gauge) strings, and their topological constraints.Cosmic strings are topological defects that may have formed during phase transitions in the early universe, analogous to vortex lines in liquid helium or flux tubes in superconductors. They are predicted by some unified theories of particle interactions and could explain large-scale structures in the universe. This review covers the background from particle physics and cosmology, the dynamics and interactions of cosmic strings, their formation and evolution in the early universe, observational implications, and the current status of the theory. Cosmic strings are massive objects with very high energy per unit length, and their gravitational effects can explain the observed fluctuations in the cosmic microwave background and matter distribution. The review also discusses the different types of cosmic strings that can form in various field theories, including global and local (gauge) strings, and their topological constraints.