This document presents the proportionality theorem and its converse. The proportionality theorem states that if a line is drawn parallel to one side of a triangle, then it divides the other two sides proportionately. The converse states that if a line divides any two sides of a triangle in the same ratio, then the line is parallel to the third side. The document provides constructions and proofs of both the theorem and its converse using ratios of corresponding parts of triangles.