IAU Transactions XXVIB contains the Proceedings of the IAU XXVII General Assembly held in Prague, 14-25 August 2006, hosting a total of 2412 participants from 73 countries. The Assembly featured a rich scientific programme, comprising 6 Symposia, 17 Joint Discussions and 7 Special Sessions. During the programme about 650 papers were presented and more than 1550 posters displayed. The Proceedings of the 6 Symposia have been published in the Proceedings of the IAU Symposia Series, and the proceedings of the Joint Discussions and Special Sessions feature in IAU Highlights of Astronomy, 14. Together with those 7 volumes, these Transactions cover the entire General Assembly. In addition to the scientific programme, the XXVI General Assembly hosted the regular Business Meetings of the EC, the 12 Divisions, 40 Commissions and 75 Working Groups. This volume records the organizational and administrative business of the XXVI General Assembly and the status of the IAU membership.