The Rule of Lenity is a principle of statutory construction that requires courts to resolve ambiguities in criminal statutes in favor of the defendant. The rationale is twofold. First, it ensures that citizens have 'fair notice' of what conduct is prohibited; it is considered unjust to punish someone under a law so vague that its meaning could not be clearly understood. Second, it maintains the separation of powers by ensuring that the legislature, not the judiciary, defines crimes and punishments. If a statute can be read in two ways—one that covers the defendant's conduct and one that does not—the court must choose the narrower reading. However, the rule only applies when a statute is 'grievously ambiguous' after all other tools of interpretation, such as legislative history and context, have been exhausted. It is a 'rule of last resort' designed to protect individual liberty from the potentially overreaching power of the state.