Maximum Stress Theory, also known as the Rankine's Theory, is a principle used in engineering to predict the failure of materials under stress. It states that a material will fail when the maximum normal stress in any direction exceeds the material's ultimate tensile strength. This theory is particularly useful for brittle materials, which tend to fracture rather than deform. In practical applications, engineers use Maximum Stress Theory to design structures and components that can withstand applied loads without failing. By analyzing stress distributions, they can ensure that materials are used efficiently and safely, preventing catastrophic failures in structures like bridges and buildings.