Triangles have six measured parts: 3 sides and 3 angles. Two triangles are congruent when all corresponding sides and interior angles are congruent. The triangles will have the same shape and size, but one may have a different position than the other. The two triangles below are congruent because each pair of corresponding sides and angles is congruent.  Congruent triangles are named by listing their vertices in corresponding order.  See the drawing below for the correct listing of the vertices of the congruent triangles.


There are many different ways that triangles may be congruent without declaring all six pair of corresponding parts congruent.  The following postulates highlight the minimum amount of information needed to know that two triangles are congruent.