Plane strain analysis is pivotal in understanding material behavior under specific deformation conditions, focusing on the characterization of linear strains (εx, εy) and shear strain (γxy). This chapter explores fundamental principles governing the strain state within a material element subjected to plane stress, emphasizing analytical and graphical methods to determine principal strains and maximum shear strain orientations. Key concepts include the derivation of longitudinal strains from normal strains and the evaluation of maximum shear strain through differentiation. Practical applications span civil and geotechnical engineering, utilizing tools like Mohr’s strain circle and strain rosettes for accurate strain measurement in three dimensions. By integrating these analyses, engineers can predict and optimize material response to complex loading scenarios, crucial for designing safe and efficient structures. Understanding plane strain analysis aids in stability assessments of geological formations, tunnels, and excavations, providing insights into the deformation mechanisms essential for structural integrity. This abstract serves as a concise summary of the chapter’s content, highlighting its relevance in engineering practice and research.