When a passenger books an itinerary, the travel agent or travel website user will create a PNR in the computer reservation system it uses. This is typically one of the large global distribution systems, such as Amadeus, Sabre, or Travelport (Apollo, Galileo, and Worldspan) but if the booking is made directly with an airline the PNR can also be in the database of the airline’s CRS. This PNR is called the Master PNR for the passenger and the associated itinerary.