This chapter describes precedence and preemption in Land Mobile Radio (LMR), the primary communications medium used by First Responders worldwide. It differentiates between implicit and explicit means for achieving precedence and preemption, and describes the situational variability in priority — a fundamental characteristic of public safety emergency communication requirements. The priority mechanisms in the APCO Project 25 standards and the ETSI Trans-European Trunked Radio (TETRA) standards are described in the context of these requirements. The chapter also describes priority calling in the third-generation Automatic Link Establishment (ALE) HF radio standards, now the US and NATO standard for digital HF radio communications, often used for critical back-up communications.