Interline Agreement
A bilateral agreement between airlines that enables each to accept the other's tickets and transfer passengers and baggage across their respective networks.
An interline agreement establishes a commercial relationship between two airlines that enables passengers to travel on a single ticket across services operated by both carriers, with baggage checked through to the final destination. Unlike codeshares — which involve one airline marketing the other's flights under its own code — interline agreements enable for ticket issuance and through-processing without requiring either airline to market the other's services actively.
Why it matters
Interline agreements are fundamental to global travel connectivity. They enable corporate travellers to build itineraries that combine the networks of multiple carriers on a single ticket — providing both through-baggage checking and airline liability for missed connections — without requiring every carrier pair on the itinerary to be codeshare partners. Without interline, complex international itineraries would require multiple separate tickets, eliminating passenger protections and creating substantial baggage complexity.
How it works in practice
When a ticket is issued over an interline itinerary, the issuing airline's ticket number covers all segments, and an agreement between the carriers governs revenue proration and service obligations. At connection points, the receiving carrier accepts the passenger without re-ticketing, and baggage transfers automatically. If the first carrier causes a delay that results in a missed connection, the interline agreement defines the obligations each carrier has to the passenger for rebooking and compensation.
The takeaway
When booking complex international itineraries that combine multiple carriers, confirm that an interline agreement exists between all carrier pairs before ticketing. Itineraries built on separate tickets — even on carriers with interline agreements — may not receive the same through-baggage and missed connection protections as single-ticket interline bookings. This distinction is especially critical on thin routes where recovery options are limited.