What is jury nullification and what is the controversy surrounding it?

Jury nullification occurs when a jury acquits a defendant they believe is factually guilty because they disagree with the law, its application, or the perceived injustice of the prosecution. It has historical roots in colonial America, where juries refused to convict under the Stamp Act. Courts do not officially endorse jury nullification, judges routinely instruct juries to apply the law as given, and some states allow judges to remove jurors who indicate an intent to nullify. However, a criminal verdict of not guilty cannot be appealed by the prosecution due to double jeopardy protections, so nullification is effectively unreviewable. Advocates of jury nullification argue it is a critical check on unjust laws; critics argue it undermines the rule of law and can produce racially biased outcomes.