Frontier Airlines is an "Ultra-Low-Cost Carrier" (ULCC) that operates on a point-to-point model, which means they historically do not have traditional codeshare or alliance partners like the major players in Star Alliance or Oneworld. Unlike United or Delta, you cannot book a seamless international journey on a partner airline through Frontier's website. However, they do have a significant business relationship with their parent company, Indigo Partners, which also owns stakes in other budget airlines like JetSMART in South America and Volaris in Mexico. While not a formal "partnership" in terms of frequent flyer reciprocity, Frontier often coordinates with these airlines for market strategy. In 2024 and 2025, there was significant talk about a "merger" or closer partnership with Spirit Airlines, but after that deal was blocked by regulators and Spirit faced financial restructuring, Frontier has remained largely independent. For passengers, this means your Frontier "Frontier Miles" are only useful on Frontier flights, and you are responsible for self-connecting if you book a trip that involves Frontier and another airline.