A brief historical background traces the origin of repeat offender provisions and the term "cruel and unusual punishment" and tracks their ultimate collision in the landmark case of Rummel v. Estelle (1980). Cases in the decade that followed are analyzed, and the emerging constitutional challenge to three strikes laws under the doctrine of separation of powers is examined. It is pointed out that legislative power to enact habitual offender laws similar to three strikes statutes has rarely been rejected by courts on a constitutional basis but rather on disproportionality grounds. Given this, the focus is on the proportionality doctrine as it relates to the cruel and unusual punishment clause of the eighth amendment. The proportionality doctrine essentially prohibits a punishment more severe than that deserved by the offender for the harm caused or the act committed. The analysis of cases demonstrates that the U.S. Supreme Court has not been consistent in its standards for evaluating three strikes laws. The court has shown deference to punishment choices made by State legislatures and has sometimes bowed to political realities when resolving constitutional dilemmas. With mandatory sentences severely hampering judicial discretion, the authors contend that appellate courts may be able to assert their authority under the doctrine of separation of powers and reject provisions in three strikes laws that transfer sentencing discretion to the executive branch. 29 references and 14 notes