An antiparallelogram is a quadrilateral in which the pairs of nonadjacent sides are congruent, but in which two opposite sides intersect (unlike in a parallelogram) and are therefore not parallel.

If the lengths of the adjacent sides of an antiparallelograms stand in the root , then the center of the opposite sides form a Bernouillian lemniscate.

An antiparallelogram can be developed as a mechanical construction with joints and the terminator points of these lines. These lines can be converted into a circle.