The paper reviews the concept of target space duality and discrete symmetries in string theory, focusing on different settings. It begins with an introduction to string theory and its properties, emphasizing the correspondence principle and the role of duality in understanding the behavior of strings at different scales. The authors then delve into the duality and discrete symmetries of the moduli space of toroidal compactifications, discussing the $R \rightarrow 1/R$ duality and its implications for the partition function. They explore higher-genus partition functions and the $O(d,d,\mathbf{Z})$ duality for $d$-dimensional toroidal compactifications, identifying the generators of this symmetry group and their connection to gauge symmetries. The paper also examines duality in orbifold and Calabi-Yau backgrounds, the role of special geometry, and the impact of duality on low-energy effective actions. Additionally, it discusses duality in curved backgrounds with Abelian symmetries, including the interchange of singularities with horizons and the removal of singularities in string theory. The authors further explore the interplay between the worldsheet and target space, highlighting the connection between modular transformations and target space duality. Finally, they address various topics that are not covered in detail, such as mirror symmetry, non-standard dualities, and the application of duality to topological backgrounds.The paper reviews the concept of target space duality and discrete symmetries in string theory, focusing on different settings. It begins with an introduction to string theory and its properties, emphasizing the correspondence principle and the role of duality in understanding the behavior of strings at different scales. The authors then delve into the duality and discrete symmetries of the moduli space of toroidal compactifications, discussing the $R \rightarrow 1/R$ duality and its implications for the partition function. They explore higher-genus partition functions and the $O(d,d,\mathbf{Z})$ duality for $d$-dimensional toroidal compactifications, identifying the generators of this symmetry group and their connection to gauge symmetries. The paper also examines duality in orbifold and Calabi-Yau backgrounds, the role of special geometry, and the impact of duality on low-energy effective actions. Additionally, it discusses duality in curved backgrounds with Abelian symmetries, including the interchange of singularities with horizons and the removal of singularities in string theory. The authors further explore the interplay between the worldsheet and target space, highlighting the connection between modular transformations and target space duality. Finally, they address various topics that are not covered in detail, such as mirror symmetry, non-standard dualities, and the application of duality to topological backgrounds.