The article provides an in-depth analysis of the structural features of antibody molecules, focusing on their biological functions and potential applications. It discusses the structures of various regions of antibodies, including the variable (V) and constant (C) domains, the Fab and Fc fragments, and the hinge region. The structures of these regions have been determined using X-ray crystallography, and the article details the interactions between different parts of the antibody molecule, such as the V-L and V-H domains, C-L and C-H 1 domains, and the Fab and Fc. The article also explores the conformational changes that occur upon ligand binding, the role of the hinge region in maintaining flexibility, and the structural variations among different antibody classes and isotypes. Additionally, it highlights the importance of the hypervariable regions in antigen binding and the potential for humanization strategies in antibody engineering. The analysis is based on a comprehensive review of available three-dimensional data and aims to provide insights into the structural basis of antibody function.The article provides an in-depth analysis of the structural features of antibody molecules, focusing on their biological functions and potential applications. It discusses the structures of various regions of antibodies, including the variable (V) and constant (C) domains, the Fab and Fc fragments, and the hinge region. The structures of these regions have been determined using X-ray crystallography, and the article details the interactions between different parts of the antibody molecule, such as the V-L and V-H domains, C-L and C-H 1 domains, and the Fab and Fc. The article also explores the conformational changes that occur upon ligand binding, the role of the hinge region in maintaining flexibility, and the structural variations among different antibody classes and isotypes. Additionally, it highlights the importance of the hypervariable regions in antigen binding and the potential for humanization strategies in antibody engineering. The analysis is based on a comprehensive review of available three-dimensional data and aims to provide insights into the structural basis of antibody function.