This final project discusses the Erdos-Mordell inequality on nonconvex qua- drilaterals. The Erdos-Mordell inequality on nonconvex quadrilaterals is an extension of the Erdos-Mordell inequality on triangles. Generally, the Erdos- Mordell inequality is the ratio of the sum of the distance of a point in a triangle to each angle and each side. Therefore, the author extends the Erdos-Mordell inequa…