The 35th Saas Fee Winter School was held on 13–18 March 2005 in the skiing village of Murren ¨ in the Berner Oberland. In view of the excitement generated over the past 15 years by the discovery of the Kuiper Belt and Trans-Neptunian Objects and also by the ongoing Rosetta mission to comet Churyumov-Gerasimenko,it was decided to combinediscussionofthese pr- itive objects into one winter schoolunder the title, “Trans-NeptunianObjects and Comets. ” The aim wasto provide an overviewof these objects, to discuss their relationships, and to identify directions for future research. The school attracted over 60 students from all over the world. We were fortunate that not merely were the students able to hear a set of outstanding lectures but were also able to enjoy marvellous weather in one of the most beautiful parts of Switzerland. The organizers thank the lecturers, Dave Jewitt, Alessandro Morbidelli, and Heike Rauer, for the tremendous e?ort they made in preparing the lectures and the text for this volume. Stephan Graf, Annette Jac ¨ kel, and Jonathan Horner provided reviews, checked the text and references, and - sisted in the production. We also thank FrauStaehli and the sta? ofthe Hotel Eiger in Mur ¨ ren for the warm welcome and their generosity. We also thank Ms. Kathrin Weyeneth and Ms. Edith Hertig from the Physikalisches Institut for their secretarial support for the school. Financial assistance provided by the Swiss Society for Astrophysics and Astronomy and the European Space Agency is gratefully acknowledged.