Forget what you think you know about dark matter. After a 30-year search for a single, as yet unidentified, species of dark matter particle that would make up some 25% of the mass of the universe, physicists are starting to consider novel explanations. Some envision invisible matter hiding within the folds of extra spatial dimensions. Others suggest not one kind of dark matter particle, but numerous species inhabiting a shadow universe. Others still conjecture that dark matter doesn’t exist, and instead propose that the laws of gravity need modification. We’ll bring together leading thinkers on dark matter—the revolutionary and conventional alike—for a distinctly unconventional discussion on the dark universe.