Integral theorems are fundamental concepts in calculus that relate integrals to other mathematical properties. They help in simplifying complex calculations by connecting the behavior of functions over a region to their behavior along the boundary of that region. Two well-known integral theorems are the Fundamental Theorem of Calculus and Green's Theorem. The Fundamental Theorem of Calculus links differentiation and integration, showing that integration can be reversed by differentiation. Meanwhile, Green's Theorem provides a relationship between a line integral around a simple curve and a double integral over the plane region bounded by the curve, facilitating the evaluation of integrals in vector fields.