Frontier check-in is the initial step in air travel where passengers present themselves at the border or immigration control before departing or entering a country. This process involves verification of travel documents, such as passports and visas, ensuring compliance with entry requirements. It is a crucial phase to confirm the eligibility of travellers, preventing unauthorised entry or exit. Passengers may also undergo security checks during frontier check-in to enhance safety measures. Efficient frontier check-in procedures are essential for smooth international travel and contribute to maintaining border security.