Following a summary of the perjury problem, the author describes constitutional obstacles to prosecuting defendants who have been acquitted. A discussion of Ashe v. Swenson introduces the collateral estoppel doctrine. Using this framework, the paper analyzes the effectiveness of constitutional double jeopardy principles in balancing the anti-perjury objective with the desire to protect the innocent. The section suggests that courts better handle perjury after acquittal cases under collateral estoppel by consistently articulating and following four principles. Alternatives to the Ashe collateral estoppel approach are examined, such as barring perjury prosecutions after acquittal or conviction when the subject of the alleged perjury is the defendant's general denial of guilt. Another option considered is establishing exceptions to collateral estoppel. 160 footnotes.