Green's Theorem is a fundamental result in vector calculus that relates a line integral around a simple, closed curve to a double integral over the region enclosed by the curve. It states that the circulation of a vector field around the curve is equal to the sum of the curl of the field over the area inside the curve. This theorem is particularly useful for converting complex line integrals into simpler double integrals, making calculations easier in many applications, such as physics and engineering. It is named after the mathematician George Green, who formulated it in the 19th century.