The gravitational-physics landscape has been evolving rapidly, driven in good part by our ability to study strong-field regions, in particular black holes. Black holes are the most amazing macroscopic objects in the universe. According to general relativity, their exterior is extremely simple, while their interior holds the failure of the underlying theory. There are thus strong reasons to test black hole spacetimes, an endeavor made possible by gravitational-wave astronomy, infrared interferometry and radio very large baseline interferometry. Black hole physics is an active field of research, which witnessed a number of important results in the last few years.

In this context, the development of collaborations between research groups focused on diverse aspects of black hole physics, from theoretical to observational aspects, is crucial for the progress of the field. The series of conferences Black Holes Inside and Out is an example of the international effort to bridge different communities. Its second edition took place in Copenhagen in 2024, and gathered some of the world experts in black hole physics, numerical relativity, black hole perturbation theory, data analysis and astronomy to discuss the status of the field and prospects ahead. With about 250 on-site participants and 200 online participants, it was the largest conference devoted to the study of black holes up to date.

On the occasion of GR24/Amaldi16, all articles in this collection are free-to-read from 10 July to 10 August 2025!

This topical collection contains a series of vision documents based on presentations and discussions at Black Holes Inside and Out 2024. All invited speakers and round table moderators were invite to prepare a vision document, encouraging content over form in order to present fresh and personal perspectives. We hope that the ideas, arguments and perspectives presented in this topical collection will be a source of inspiration for new and experienced researchers alike in the years to come.

Read the summarizing Editorial: Buoninfante, L., Carballo-Rubio, R., Cardoso, V., Di Filippo, F., Eichhorn, A.: Topical Collection – Black Holes Inside and Out 2024: Visions for the future of black hole physics. Gen Relativ Gravit 57, 109 (2025). https://doi.org/10.1007/s10714-025-03444-8