Cosmic strings are topological defects that may have formed during phase transitions in the early Universe. They are predicted by some unified theories of particle interactions and could help explain large-scale structures in the Universe today. These strings are stable and may have played a role in structure formation, providing density inhomogeneities from which galaxies eventually grew. Their observational signatures are distinctive and within reach. The paper reviews the formation, dynamics, and interactions of cosmic strings. It discusses the relevant background from particle physics and cosmology, including symmetry breaking, defect formation, and the Big Bang. It covers different types of cosmic strings, such as global, local, and electroweak vortices, and their interactions with other fields. The formation and evolution of cosmic strings in the early Universe are discussed, as well as their observational implications. The paper also reviews the present status of the theory, highlighting the importance of cosmic strings in cosmology.Cosmic strings are topological defects that may have formed during phase transitions in the early Universe. They are predicted by some unified theories of particle interactions and could help explain large-scale structures in the Universe today. These strings are stable and may have played a role in structure formation, providing density inhomogeneities from which galaxies eventually grew. Their observational signatures are distinctive and within reach. The paper reviews the formation, dynamics, and interactions of cosmic strings. It discusses the relevant background from particle physics and cosmology, including symmetry breaking, defect formation, and the Big Bang. It covers different types of cosmic strings, such as global, local, and electroweak vortices, and their interactions with other fields. The formation and evolution of cosmic strings in the early Universe are discussed, as well as their observational implications. The paper also reviews the present status of the theory, highlighting the importance of cosmic strings in cosmology.