We present an operator algebraic approach to Wigner's unitary-antiunitary
theorem using some classical results from ring theory. To show how effective
this approach is, we prove a generalization of this celebrated theorem for
Hilbert modules over matrix algebras. We also present a Wigner-type result for
maps on prime C*-algebras.Comment: AMSLaTeX, 17 pages. To appear in J. Austral. Math. So