In this unit, students begin by reasoning about the relationships between congruent parts of figures, and congruent figures. They use transformations as tools for reasoning and generalizing. Students use transformations to prove three theorems about triangle congruence: Side-Angle-Side Triangle Congruence, Angle-Side-Angle Triangle Congruence, and Side-Side-Side Triangle Congruence. As students prove new theorems, they apply those theorems to prove results about quadrilaterals, isosceles triangles, and other figures. Finally, students have a chance to apply their skills to conjecture and explore congruences and properties of quadrilaterals.