Allegiant Airlines is a popular low-cost airline that operates both scheduled and charter flights to various destinations across the United States, Mexico, and the Caribbean. Allegiant Airlines Book a Flight Airlines, customers can visit the airline's official website or mobile app.The process to book a flight with Allegiant Airlines is straightforward and user-friendly. Customers can search for available flights by selecting their desired origin and destination, travel dates, and the number of passengers. Once the search is complete, customers can choose from a list of available flights and select their preferred departure and arrival times.