Euler-Bernoulli beam theory is a fundamental principle in structural engineering that describes how beams bend under load. It assumes that the beam is slender, meaning its length is much greater than its cross-sectional dimensions. The theory simplifies the analysis by considering only the bending deformation, neglecting shear deformations and axial effects. The theory is based on the relationship between the applied load and the resulting deflection of the beam. It uses the moment-curvature relationship, which states that the curvature of the beam is proportional to the bending moment. This allows engineers to predict how beams will behave under various loading conditions, ensuring safe and efficient designs.