These Transactions provide a record of the organisational and administrative activities of the IAU XXX General Assembly, which took place in Vienna, Austria, in August 2018. They report and record all of the essential decisions taken by the governing body of the IAU. These include the approval of the financial accounts and of the proposed budget for the next three years, the admission of new national and individual members, the Divisions, Commissions, and Working Groups, the new Officers and Executive Committee, and the approval of Resolutions, as well as opening and closing ceremonies and other events. Focus Meetings are published in the 'Astronomy in Focus' series, and each of the six Symposia that took place has its own Proceedings. The world was forever changed by the COVID-19 pandemic shortly after this General Assembly, contributing to the delay in this volume's publication.