A quadrilateral with two pairs of parallel sides is called a parallelogram. The height of a parallelogram is always perpendicular to its base.

All parallelograms have the following properties.

1. The opposite sides are congruent by the Parallelogram Opposite Sides Theorem.
2. The opposite angles are congruent by the Parallelogram Opposite Angles Theorem.
3. The diagonals bisect each other.