6 The Impact of Third- Party Internet Sites on the Hotel Guest Journey Niels van Felius, Elena Cavagnaro and Marit de Vries Learning goals This chapter focuses on the sustainability challenges that arise from the increased infu- ence of Third-Party Internet sites on the guest journey, in particular during the gathering of information and judgement of alternatives phase. After studying this chapter, readers will have the ability to: 1 Defne the growth in the use of online information communication technology from a hotel perspective; 2 Describe the guest journey focussing on how a hotel guest uses a Third-Party Internet site (TPI) as a booking tool; 3 Describe the main technology for data gathering behind TPIs, and the resulting bubble efect; 4 Explain the sustainability challenges connected with the bubble efect; 5 Identify tools to address the challenges of the bubble efect considering also best- case examples. Introduction Reservations are essential for hotels to plan their operations. When considering reservations for their planning, hotel departments usually refer to the reserva- tion horizon, that is the number of rooms booked on a day in the future, and the predicted pick-ups, that is the number of room reservations a hotel expects to get confrmed over a certain period. These fgures are used to decide upon, for exam-