Fubini's Theorem is a fundamental result in calculus that allows us to evaluate double integrals by iteratively integrating with respect to one variable at a time. This theorem states that if a function is continuous over a rectangular region, the order of integration can be switched without affecting the result of the integral. In practical terms, Fubini's Theorem simplifies the process of calculating areas and volumes in higher dimensions. By breaking down complex integrals into simpler, one-dimensional problems, it provides a powerful tool for mathematicians and scientists working in fields such as Physics and Engineering.