If there is no online ticketing agreement, two tickets must be issued separately and passengers must collect their luggage and bring it to the connecting company for check-in. Routes with such interline connections are riskier for travelers, as the second airline may not experience delays or problems with the arriving flight, and in case of loss of the route, it is less likely that there will be a free rebooking. There may also be a problem if the luggage is lost and the traveler wants it to be sent to them later. If two airlines enter into an interline agreement, this is the most fundamental form of partnership you will find. Essentially, it allows passengers to book itineraries with multiple airlines with less effort than booking them individually. Interlining, also known as interline ticketing and interline booking, is a voluntary commercial agreement between individual airlines to process passengers traveling on routes requiring multiple flights with multiple airlines.  Such agreements allow passengers to switch from one airline flight to another without having to pick up their luggage or check in again.