  This paper considers the construction of isodual quasi-cyclic codes. First we
prove that two quasi-cyclic codes are permutation equivalent if and only if
their constituent codes are equivalent. This gives conditions on the existence
of isodual quasi-cyclic codes. Then these conditions are used to obtain isodual
quasi-cyclic codes. We also provide a construction for isodual quasi-cyclic
codes as the matrix product of isodual codes.
