The 15th International Conference on the Theory and Application of Diagrams takes place on 25-28 August 2026 at Tallinn University of Technology, Estonia. Registration to the conference is now open. To register, please visit: https://diagrams-conference.org/2026/registration/ Registration to the conferences gives access to all talks, including three keynotes (by Jessica Carter, Peter Cheng and Fabio Zanasi). Registration also gives access to the tutorials and the graduate Symposium. All participants will furthermore receive a free copy of the Diagrams conference proceedings (published by Springer). For more information, please visit the conference website: https://diagrams-conference.org/2026/ Registration is open for everyone. We hope you will join us at the conference! Best wishes, The Diagrams 2026 organizing team